Star In A Star

Star Noon 3 of 3: See Sidereal Time in the Sky

Tue, 31 Mar 2026 12:00:00 GMT

Sidereal Time - a 3-part series

In the previous post, we followed Sirius from its alignment with the Sun in July to its midnight "star noon" on New Year's Eve — watching the 3-minute-56-second daily drift play out across the seasons. Now, let's step outside and see sidereal time for ourselves.

See sidereal time in the sky

Look up at the night sky at midnight on a balmy summer evening. If you are lucky, there are a few hundred visible stars in the sky. Depending on the "clock time" and the date on the Earth, a specific group of stars and their constellations is in view. At midnight each day we get a specific window onto the stars - many stars are visible in the sky, but most are below the horizon, behind the Earth. We see stars rising in the east and stars setting in the west.

Take a snapshot of this starry midnight sky and hold it in your mind.

The Earth continually rotates so the stars move in our sky all through the night and continue the next day. At the same "clock time" tomorrow the entire starry half-dome of stars will be visible again, but they will appear to have moved very slightly. Each day, the stars appear to move a little bit toward the west because of the progression of the Earth's orbit along its "track." It is this progression that makes the stars seem to rise earlier each day.

Snapshot of the midnight sky

Here's a good way to think about sidereal time: snapshot the midnight sky every night for a year, then play it back as a time lapse movie. What would you see?

If we "snapshot" the midnight sky (at midnight the Sun crosses the anti-meridian... this happens once every 24 hours) we will see a slow westward movement of stars. The stars move steadily westward because the Earth's "midnight window" moves eastward (counterclockwise) in orbit.

Our Earth-bound, nighttime window on the sky changes all year long. It's as if we were in a strange train on a long circular track. As seen from above... day (the Sun) is always visible out the left side, night is visible out the right.

Stars at Opposition

Seen from "above" the solar system, the Sun, the Earth and a star make a straight line; when a star crosses the anti-meridian at midnight that star is at opposition. Stars can cross the anti-meridian at any location from north to south.

Familiar stars that appear along the Zodiac or the celestial equator help us ponder sidereal time.

There is one starry Zodiac region in particular that plays the role of sidereal time "zero": the spring equinox point which is currently "in" the constellation Pisces. When this point crosses your meridian, sidereal time resets to zero — like noon on a solar clock.

Where sidereal time begins (how to tell time by the stars)

To get to the zero start time in sidereal time we ignore the Sun. We set our clocks to sidereal time zero by the meridian crossing of the stars.

The beginning of sidereal time is the moment the spring equinox sky location (where the Sun crosses upward along the ecliptic past the celestial equator - the so-called "first point of Aries) crosses the observer's local meridian. The snapshot at this moment is sidereal time "zero."

You can chase this sidereal time frame over the course of a year (orbit) by changing the time you observe or by changing your location on the surface of Earth.

Telling time by the stars

The circumpolar constellations can tell you the time at night - the solar time. All you need is an ancient device called a Nocturnal, a clear view of the northern sky, and the date.

An illustration showing the Nocturnal, the observer's eye, and the stars. Johann "nojhan" Dréo, CC BY-SA 3.0, via Wikimedia Commons.

The Nocturnal is an ancient device that helps you to find the solar time from the position of circumpolar stars. But, this is using the stars to tell solar time - it's fascinating and useful, and it illustrates the point of this article: the stars move in a predictable, yearly motion that can be used to tell time. Sometimes you want to tell solar time but sometimes you want to tell sidereal time.

Summary of sidereal time

Sidereal time is time-keeping based on the stars as opposed to the Sun.

A sun-clock is a normal clock - it keeps track of the Sun and the 24 hour day. A star clock keeps track of where the Earth is in its yearly orbit.

Another word for a time-keeping machine that tunes itself to stars is GPS. Well, GPS actually uses quasars which are not technically "stars."

Nocturnal - a timekeeping device like a sundial but for the night and the stars.

References

Sidereal Sky removal map generated by the Solar Mass Ejection Imager (SMEI).

Astronomy 505 course with notes about time from New Mexico State University.

A NASA mini-article "Telling the time by the stars" that gives the value 1.0027

A very comprehensive page about sidereal time including lots of images of sidereal clocks.

A well-written introduction to the physical aspects of sidereal time.

An article from Harvard with some clever tricks about figuring out sidereal time.

An interactive tool to help you visualize sidereal time alongside solar time.

Previous: Follow Sirius Through the Year

Star Noon 2 of 3: Follow Sirius Through the Year

Fri, 27 Mar 2026 12:00:00 GMT

Sidereal Time - a 3-part series

A sidereal clock gets its time from the position of faraway stars - not the Sun. Each 24 hour period all of the stars slide one-by-one across the meridian - each creating their own "noon." There is a "Sirius noon" and a "Vega noon" and a noon for each of the thousands of visible stars. Some of the star "noons" happen at midnight, but some of them happen when the Sun is up.

The Sun is too bright; it blocks out the stars - let's trick the Sun

But during the day even these bright stars are too dim to compete with the Sun. The stars are "up there" behind the Sun in the sky, but they cannot be seen: the Sun is too bright. During the day we cannot tell when a star crosses the meridian so we cannot tell sidereal time when the Sun is in the sky.

However, the Sun only blocks a sliver of the sky at any one time and we can use midnight to mark meridian star crossings. If we stay up all night, we can see most of the stars and those visible stars can be used as a sidereal clock; we just have to observe them. Let's visualize the bright star Sirius lined up with the Sun on the meridian together.

Sun and Sirius shown crossing the meridian at the same time in July. The purple line indicates the shared meridian. This image is what the sky will look like on July 1, 2021. It repeats every year the same way.

The Sun and Sirius, the Dog Star

This "lining up" of the star and the Sun means that Sirius noon and Solar noon happen at the same time. The Sun and the star travel together through the sky. Sirius is "there" closer to the southern horizon than the Sun. But it is invisible during the day because it is so much dimmer than the Sun. This almost perfect alignment of the Sun with the dog star Sirius happens on July 1st.

But, each day the stars "travel" a little bit faster than the Sun so they create a "star day" that is slightly shorter than a solar day. Star noons happen once every 23 hours, 56 minutes, and 4 seconds. This is 3 minutes and 56 seconds faster than the Sun. This "speed" difference makes the stars all appear to move faster than the Sun. So, each day the star Sirius moves slightly westward and precedes the Sun by a larger and larger slice of the sky.

Sirius crosses the meridian before the Sun just a month later in August.

Larger slices of the sky

This means that, eventually, Sirius will spend more and more time in the night sky and its meridian crossings will become visible in the night sky. Sirius is seen first at dawn during heliacal rising in August and then later (by late fall) solidly in the dark sky of night. Eventually, Sirius will cross the anti-meridian (the opposite point to the Sun's current meridian) at midnight and have its "star noon" (its meridian crossing) at solar midnight.

For Sirius, this happens at the New Year on December 31st around midnight. On this date Sirius is separated from the Sun by 180 degrees. At New Year's Eve you are literally turning your back on the Sun when you look up at Sirius at midnight.

"Sirius noon" - on January 1st at midnight, Sirius has its own "noon" along with Mebsuta (ξ Gem) and Alzirr (ε Gem)

Which star is the main star? Which marks the start of the sidereal year?

To fully understand sidereal time, it helps to imagine you can see all the stars in the sky both night and day. Imagine being inside a giant celestial sphere. You look up, and you see the sky as if it is a giant, transparent shell.

Stars move across the sky during the course of a night and day, but they also move over the course of a year. Bright stars rise each minute, cross the meridian, and set. Each star crossing the meridian creates its own star noon. Once per year every star rises and sets together with the Sun. The stars can be thought of as a celestial sphere with the Earth at the center. But, there is no "main star" that marks the start of the sidereal year.

The celestial sphere is a map of the year

It's fun to imagine sidereal time because it helps you to see the celestial sphere as a "map of the year." Thinking in sidereal time helps you to see the Sun anew - a blinding light in the sky that hides the stars during the day and the source of "noon."

By learning sidereal time you see that the Sun is independent from the stars, not moving with the celestial sphere but across it. Also, as a bonus, you can get more familiar with the words meridian (noon) and anti-meridian (midnight).

For instance, a star that first appears at the meridian at sunrise is a star that will join the Sun in 9 months. Every star moves westward day-by-day and it takes 12 months for the Sun to block out each one on its way through the sliver of stars in the Zodiac.

Now that you can see the celestial sphere as a map of the year, let's step outside and learn how to see sidereal time in the night sky.

Previous: Star Noon and Sun Noon Next: See Sidereal Time in the Sky

Star Noon 1 of 3: Star Noon and Sun Noon

Mon, 23 Mar 2026 12:00:00 GMT

Sidereal Time - a 3-part series

There are two skies: the sun (solar) sky and the starry (sidereal) sky. You can tell time by observing objects in both skies.

The Sun can be the basis for a clock; the stars can be the basis for a clock. Once a year solar clocks and sidereal clocks align with each other - telling the "same" time. This happens at the autumnal equinox, when the Sun's right ascension is 12 hours. But, then stellar time and solar time drift apart.

Sidereal time is weird. Sidereal time (sai·dee·ree·uhl) means "star time." Sidereal time-tracking challenges you to orient to the celestial sphere. It means you ignore the Sun and use the stars as your time keeper! You place the Sun inside the celestial sphere and see each layer of that placement as the foundation of a viable clock. Set a clock to "star time" (not solar time) and you'll be a better astronomer.

Star noon

Star noon is a two word description of sidereal time.

Sun noon (solar noon) happens when the Sun crosses your meridian.

Star noon (stellar noon) happens when a star crosses your meridian.

There is only one solar noon but there are many, many stellar noons.

A star crossing the meridian can be said to be at "noon" in the sky. While "noon' normally refers to the position of the Sun in the sky, we can say "star noon" as a shorthand for "star crossing the local meridian."

Every star's "noon" moves slowly around the 24 hour day through the year. A star's "noon" happens near a solar noon once per year. If this seems confusing right now, don't worry! We are going to look at stellar time more deeply and will see how the Sun and stars move (mostly) independently from each other.

Stars have their own "noon"

This is the concept of sidereal time: the stars have their own "noon" each day - but while the Sun's noon (meridian crossing) is the noon, the stars have to make do with a shifting noon. This shift of the sidereal time happens because solar clock time is determined by the Sun's apparent position in the sky, not any other stars.

If you track the sky by sidereal time, you have to observe the sky through the course of an entire year. The stars will appear in the same place the next day but you have to look up 3 minutes and 56 seconds earlier each day. This time shift happens because the Earth travels in its orbit. We get a slightly different "snapshot" of the sky each night.

Let's first talk about how clocks work with the Sun so that we can understand how sidereal clocks work with stars.

The place named "noon" and the perfect clock

The perfect clock on the surface of the Earth precisely matches "clock noon" to the Sun's meridian-crossing every day. But,* the perfect clock does not exist.* There is no clock that matches the ebbs and flows of natural time in all locations. For one thing, moving east or west on the surface of the Earth - even just at walking speed - changes the time. Also, in order to use a precise clock we also have to know the exact date.

But, let's avoid complications and imagine that we have a perfect solar clock.

A clock is a machine tuned to the Sun

Jean Housen, CC BY-SA 4.0, via Wikimedia Commons

A clock is a machine that is tuned to the Sun. A normal clock gets its time from the Sun. The moment the Sun crosses the meridian (an imaginary line that divides the eastern from the western the sky) we say it is noon. A normal clock's noon (12 o'clock) coincides with this sky event.

Our clock time is set to match the way the Sun appears to move across the sky throughout the day (and night). When you say "same time tomorrow" it means "same Sun position tomorrow."

A sidereal clock gets its time from the stars

Sidereal Clock. Notice the Zodiac symbols around the top clock. Original from Wikipedia.

In contrast, sidereal time is set based on the way* stars* appear to move. That is a different reference frame because the stars arrive at the same place in the sky 3 minutes and 56 seconds earlier each day. If you said "see you the same sidereal time tomorrow" it would mean "let's meet up about 4 minutes earlier tomorrow."

The clocks based on the two sets of sky motions drift apart over the year and then meet again each autumn.

In the next post, we follow a single star — Sirius, the Dog Star — through the year, and see this drift play out in the real sky.

Next in series: Follow Sirius Through the Year

16 Laps Around the Galaxy, 20 Laps to Go

Sun, 15 Mar 2026 12:00:00 GMT

We are on lap 16.

Not us, personally, in our short human lifetimes, but the Earth beneath our feet, the Sun above our head, and the entire solar system. All of it is circling the center of the Milky Way Galaxy.

Scientists estimate that one full orbit takes about 230 million years. The Earth is roughly 4 billion years old. That means our planet has completed about 16 laps around the galaxy so far.

Sixteen trips around the galaxy.

The solar system's orbit around the Milky Way center. One full lap takes about 230 million years.

What does one lap look like?

It is hard to feel a galactic orbit. The Earth's daily rotation takes 24 hours and we can see it in every sunrise. The yearly orbit around the Sun takes 365 days and we feel it in the seasons. But a galactic orbit? 230 million years is so long that the dinosaurs had not yet appeared when the Earth last crossed the spot where it is now.

Think about that for a moment. The last time the solar system was here, at this same position in its orbit around the galaxy, there were no T. rex, no flowering plants, no birds. The continents were in different places. The Atlantic Ocean did not exist. One full lap ago, the Earth was an almost unrecognizable place.

Earth one lap ago, with all the continents fused into Pangaea, and Earth today.

And yet, the orbit is real. The Sun moves through the galaxy at roughly 200 kilometers per second, carrying all of us with it. That is about 720,000 kilometers per hour. But the galaxy is so vast that even at that speed, one lap takes 230 million years.

What we are orbiting

At the center of the Milky Way sits a supermassive black hole called Sagittarius A*. It has the mass of about 4 million Suns packed into a region smaller than the orbit of Mercury. We cannot see it directly, but its gravity shapes everything around it. It is the anchor.

Sagittarius A* does not do this alone. The combined mass of all the stars, gas, and dust between us and the center contributes to the pull that holds the solar system in its orbit. But the black hole is the heavy center that the whole structure revolves around. Without it, the galaxy would not hold its spiral shape. The arms would drift apart. Our orbit would not exist.

We are 26,000 light-years from that center, moving along one of the spiral arms at 200 kilometers per second. Close enough to be held. Far enough to be safe. A comfortable distance for a 230-million-year lap.

Counting laps

At 4 laps per billion years, 4 billion years gives us about 16 completed laps. Sixteen times the Earth has traced this immense circle. Sixteen times the Sun has returned to roughly the same neighborhood in the galaxy.

Each lap, the Earth was different. On some early laps, there was no life at all. On later laps, the oceans filled with strange creatures. On recent laps, forests grew and fell and grew again, ice sheets advanced and retreated. On the most recent fraction of a lap, humans appeared, looked up, and started wondering about all of this.

20 more to go

Scientists estimate that the Sun will continue to shine for about 5 billion more years before it exhausts its fuel and swells into a red giant. Five billion years at 4 laps per billion gives us roughly 20 more galactic orbits.

Twenty more laps. That is what remains.

16 laps completed, 20 to go.

We are not at the beginning and we are not near the end. The Earth is somewhere in the middle of its total journey around the galaxy, lap 16 of about 36. Not quite halfway.

There is something grounding about this. We live on a planet that has been around its galaxy many times and will go around many times more. We are not newcomers.

Next time you look up at the Milky Way — that faint band of light that is the edge-on view of our own galaxy — remember that you are not just looking at it. You are inside it, moving through it, rounding a curve that takes 230 million years to complete.

Lap 16. Twenty more to go.

Vega–Capella anchor the equinoxes

Fri, 13 Mar 2026 14:00:00 GMT

Vega–Capella anchor stars

Bright stars can act as pointers to significant locations in space — places that have no star of their own, like the equinox points where the Sun crosses the celestial equator. You can't see these points directly, but you can aim at them using stars you already know.

Observe the autumn equinox point in spring

Use Vega and Capella as “anchor stars” to help aim at the equinox points in the sky. When you can see both Vega and Capella low on the northern horizon, imagine a straight line between them. That Vega–Capella line is your baseline.

Add Caph (in Cassiopeia) as a third bright anchor. Using Caph + the Vega–Capella baseline, you can make a steady sight line that points toward the spring (vernal) equinox point.

Observe the spring equinox point in autumn

About six months later, use Phecda (in the Big Dipper) lined up toward Zavijava (in Virgo) as a strong marker for the fall (autumnal) equinox point.

Note that as the Earth turns, Vega and Capella line up so their line looks almost parallel to the horizon twice each day, but you’ll usually only be able to see those moments at night.

Notes

The equinox point is not a star. It’s a special spot in the sky.
Do it when the stars are low in the same place each time to keep it consistent.

Fifth Friday and the Full Moon

Fri, 13 Mar 2026 12:00:00 GMT

Let's meet on the fifth Friday of the month, let's make it the next one with a full moon. When exactly is that? How old will I be?

It sounds less like a plan than an incantation. It has the feel of folklore, or a line from a song, or a date chosen for reasons too old to explain. And yet it is perfectly real.

The fifth Friday

A 31-day month is not four neat weeks. It is four weeks plus three extra days. Those extra days spill over. They often create a fifth Monday, a fifth Thursday, a fifth Friday.

A fifth Friday is not especially rare. It appears four or five times in many years, simply because calendar months are not made of four tidy weeks. A 31-day month contains four full weeks plus three extra days, which means three weekdays will occur five times.

That is how 2026 ends up with fifth Fridays on:

January 30,
May 29,
July 31, and
October 30.

There is nothing celestial about that part. A fifth Friday is a feature of the human grid we lay over time: month names, week lengths, the repeating rhythm of workdays and weekends. It belongs to the architecture of the calendar. This is the part I love most: the sky is not using our calendar. The Moon is not aiming for Friday. Friday is our idea.

A full moon belongs to something older

The lunar cycle does not reset at the end of a month or pause for the convenience of our bean counters. The Moon keeps its own schedule as it moves through its orbit around Earth, returning to full on a rhythm that does not match our calendar months. That slight mismatch creates all sorts of small wonders: months with no full moon, months with two, and more rarely, dates when a full moon lands on a fifth Friday.

It's a meeting point between two systems of timekeeping that were never designed to agree. One is civil and practical. It organizes appointments, payroll, school terms, rent, and routine. The other is observational and physical. It is written in light and shadow, in the geometry of the Sun, Earth, and Moon. Most of the time, these systems pass through one another without comment. Then, every now and then, they briefly align.

A few exact examples of that overlap are:

September 29, 2023;
December 30, 2039;
August 29, 2053;
and March 31, 2056.

Those dates feel memorable not because they carry any hidden power, but because they reveal the juncture between natural cycles and human order. They show us, for a moment, both rhythms, in sync.

"The fifth Friday with a full moon" sounds ceremonial because it joins two different kinds of recurrence: one invented, one inherited. One came from the need to organize and "square off" society; the other from looking up with wonder.

Astronomy often lives at grand scales: nebulae, galaxies, black holes, distances so large they resist intuition. But astronomy also lives here, in the ordinary language of dates and evenings and the familiar face of the full moon. It lives in the moments when our paper calendar and the sky happen to rhyme.

A delightful, luminous, lilting orbit

So yes: let's meet on the fifth Friday, one with a full moon too.

Not because the orbit arranged it for us "just so" – but because it is delightful when our way of counting days briefly falls into step with that older, luminous calendar overhead.

A full moon is natural; a fifth Friday is administrative; together they become poetry.

Let's meet!

Moon Phases Names - an easy way to remember

Sun, 12 Jan 2025 21:57:52 GMT

The 8 Moon Phases Names

Here are the "official" 8 Moon Phases in order:

New - the new moon is not visible
Waxing Crescent - the Moon starts growing
First Quarter - the moon looks like half a circle
Waxing Gibbous - still growing
Full - we see the entire circle of the Moon lit up
Waning Gibbous - the Moon starts shrinking
Third Quarter - again only half a circle is visible
Waning Crescent - the Moon is about to disappear
New (again) - the new Moon is not visible

The Moon Phases in left-to-right order with the official names - you might sometimes see "last quarter" used where the correct name is "third quarter."

Moon phase names - The Moon Hat

The Moon Hat is a science gift for the curious. Precisely placed Moon phases "point" to the Moon in the sky and help you find it day or night.

Buy a Moon Hat (a great science gift made by Star In A Star - order today and get FREE shipping), you can learn all about the Moon phases every time you wear the hat. The Moon Hat is a scientific "moon-finder" instrument that helps you locate the Moon in the sky day or night.

The Moon Hat is one in a line of "Science Clothing - clothing that makes you smarter!" It was invented and is made and sold by Daniel Cummings - the owner of this website and the author of this blog.

Play with the Moon Phases in order from right to left

<div id="moon-emoji-sketch"></div> <script> (()=>{let em=[['🌑','New'],['🌘','Waning Crescent'],['🌗','Last Quarter'],['🌖','Waning Gibbous'],['🌕','Full'],['🌔','Waxing Gibbous'],['🌓','First Quarter'],['🌒','Waxing Crescent'],['🌑','New']], d=document.getElementById('moon-emoji-sketch'),c=d.appendChild(document.createElement('canvas')),x=0; c.width=c.height=300;let g=c.getContext('2d');g.textAlign='center';g.textBaseline='middle'; c.onmousemove=e=>x=e.offsetX; let C=(v,a,b)=>v<a?a:v>b?b:v,M=(v,a,b,c,d)=>c+(v-a)(d-c)/(b-a); !function r(){ g.fillStyle='#000';g.fillRect(0,0,300,300); g.strokeStyle='#fff';g.strokeRect(3,3,294,294); g.fillStyle='#fff';g.font='18px system-ui'; em.forEach((e,i)=>g.fillText(e[0],i32+26,230)); let m=~~M(x,0,270,0,8),i=C(m,0,8); g.font='126px system-ui';g.fillText(em[i][0],150,100); // +50px down (50 -> 100) g.font='18px system-ui';g.fillText(em[i][1],150,200); g.fillStyle='dimgray';g.beginPath();g.arc(m*32+27,245,2.5,0,7);g.fill(); // 2px left (29 -> 27) g.fillStyle='gray';g.fillText('Move the mouse left and right.',150,280); requestAnimationFrame(r) }()} )(); </script>

This is a "physical model" of the Moon's phase changes. Move the mouse Right to Left.

Each day the Moon moves leftward (east) through the sky - for people looking at it from the northern hemisphere. As it moves through a 29.5 day orbit, the Moon grows and then shrinks again. It starts New, grows Full, then wanes to New again.

Move your mouse from right to left on these Moon Phase emojis to recreate the correct order of phases as the Moon moves in its orbit.

Remember the 8 Moon phases

The main Moon Phase cycle is very simple and symmetrical:

New -> WAXING -> Full -> WANING -> New.

Studying for a Moon Phases quiz?

You can shorten the Moon phase names to: "Never can quit getting food" = NCQGF

NCQGF = New, Crescent, Quarter, Gibbous, Full

Just remember that sequence of letters: NCQGF. That gives you the order of the waxing phases, then reverse it to get the waning phases: FGQCN. The good thing about this sequence of letters is that you just have to memorize it one way! During your Moon Phases quiz you can write it down and then reverse it.

FGQCN = Full, Gibbous, Quarter, Crescent, New

The list of 8 Moon phases to memorize

The Moon Phases happen in a cycle that repeats.

New, wax crescent, 1st quarter, waxing gibbous,
Full, waning gibbous, 3rd quarter, waning crescent,
New (again).

What is Waxing and What is Waning

Waxing = growing

Waning = shrinking.

You can remember wax and wane because wax is growing like putting layers of wax on something. Like in the old Karate Kid movie "wax on."

A mnemonic - DOC - will help you learn the Moon phases names

Here's a good way to remember the order of the Moon phases if you have to choose the phase name based on an image of the phase: DOC.

The three letter word DOC is a good mnemonic for remembering the Moon phases names and how they grow first and then shrink. It's a "shape-ronym" - I have a feeling I just invented that name - it's where the letter shapes help you remember something.

If the Moon phase is shaped like the letter D that means it is growing (waxing). If the Moon phase is shaped like the letter C that means it is shrinking (waning). If it's shaped like the letter O - it is full: in between waxing (D) and waning (C).

You can remember that "light starts on the right" of the waxing crescent, then it grows to full, then shrinks to the crescent where "the only light left is on the left."

NOTE: if you are in the southern hemisphere the mnemonic is COD because the Moon is Upside Down.

Start - The Waxing Moon D

As soon as the growing (waxing) Moon becomes a Waxing Crescent Moon we can see that the shape of the lit up part of the crescent can make the capital letter D. As the Moon grows through to Waxing Gibbous phase it is still shaped like a capital D.

Middle - The Full Moon O

The Full Moon is shaped like a capital O.

End - The Waning Moon C

The waning phases make the shape like a capital C.

Moon Phases Names patterns

Here are a some interesting patterns in the Moon phases names.

The cycles repeat - New to Full to New (again).
The Moon grows (waxes) and then shrinks (wanes) again. Why doesn't the Moon grow to a Full Moon and then just blink out and start again... or maybe it could stay the same shape all the time... so many possibilities... why does it grow and then shrink?
The New Moon is the commonly accepted "beginning" and also the "end" of the cycle.
Gibbous is a really weird word - it is from the Latin "hunch or hump."
There is a first and third quarter, but no 0th or 4th quarter.
Wax and Wane are more weird, old words - they are words originally handed down from the ancient language Sanskrit that made their way through history to old German and finally to old English.

The Moon's Missing Quarters, weird

What's the deal with First Quarter and Third Quarter?

Astronomy names can be unusual sometimes. The Moon has a "First Quarter" and a "Third Quarter"... but it has no "Second Quarter" and no "Fourth Quarter" or "Zeroth Quarter."

The Second Quarter would be the Full Moon but we don't use that name. But, then what would the New Moon be called? Is it the Zeroth (0th) quarter or the Fourth (4th) Quarter? Is the New Moon the beginning or the end of the orbit? Based on the more common name it should be called the zeroth quarter because it is the "New" part of the orbital cycle. Zero = nothing and during the New Moon there is no Moon visible.

The Moon is at "First Quarter" but its shape is half a moon!

This is kind of strange too: the moon looks like a "half moon" two times during the moon's cycle. It is a half moon as it grows (waxes) and becomes a half moon again when it shrinks (wanes). The moon is clearly showing half a moon.

Confusingly, astronomers actually call the "half moon" a "quarter moon."

Regular people call it a "half moon" even though astronomers call it a quarter moon. We should all call the first quarter moon the "waxing half moon" and the third quarter moon the "waning half moon." But, these are not common names at all!

Actually, I'd like to call the first quarter (waxing half moon) the "Earth's tail moon" and the third quarter (waning half moon) the "Earth's nose moon." These names point out a neat fact about the Moon's orbit - it crosses the Earth's orbit twice a month - once at first quarter, then again at third quarter.

Anyway, why do astronomers call a half moon the quarter moon?

Astronomers use the quarters to talk about the orbit of the Moon and its location in the orbital path. The name "quarter" says "the Moon is a quarter of the way through its orbit now."

The moon phases names are odd

How to remember the phases of the moon? Let's face it, the Moon phases are named with really old words - the kind of words we don't really use anymore, but we are stuck with them because the Moon is kind of important and we can't just ignore it.

Here is a good way to think about the words tied to the phases of the Moon. These words describe 4 things: the "age" of the Moon, the apparent "shape" of the Moon, its direction of growth, and its location in its orbit around the Earth:

Age, Shape, Growth, Orbit

These words describe the "Age" of the Moon: new moon, quarter moon,

These word describe the "Shape" of the Moon: half moon, full moon, gibbous moon and crescent moon.

These words describe the "Growth" of the Moon: waxing (growing) moon and waning (shrinking) moon,

This word describes the Orbit of the Moon: quarter moon.

The Moon moves in orbit

Each day, the Moon moves along an orbit that carries it around the Earth. It takes about 29.5 days for the Moon to make a complete trip from one New Moon to the next New Moon.

Each day the Moon moves about 1/27th of the sky: 360˚/27.5 days = 13.1˚ per day. This is about the distance between your index finger and your pinky held up at to the sky at arms length. The Moon moves eastward each day toward the dawn.

The Sun is always lighting up half of the Moon.

The light of the Sun always comes from one place - the Sun! Light from the Sun hits the Moon and lights up half of the Moon at all times.

However, it is not always the same half that we are looking at from Earth. The Moon shows us only part of its bright side for most of its 29.5 day orbit. It's only during the Full Moon that we see the entire "half" illuminated Moon.

The Moon seems to change shape

The Moon changes phase because the Moon moves. As it moves, we see different light from the Sun reflecting off the Moon every second. The amount of light we can see changes every second as it moves through space around the Earth.

A fun and easy thing to watch with a telescope is to look at the Moon and see the Sun's light casting changing shadows on the Moon.

Summary

This article summarized the names of the phases of the Moon and pointed out some interesting patterns. You learned a mnemonic (shape-ronym) device to help remember the order of the Moon phases.

Comments

starinastar - November 27, 2018 at 10:30 AM

A recent visitor told me about this fun video: Mr. Lee Phases of the Moon Rap. https://www.youtube.com/watch?v=79M2lSVZiY4

Scotty D - February 19, 2025 at 6:10 AM

"Light Right" Delight :) DOC

Analemma answers the question: "What time is it at noon?"

Sun, 12 Jan 2025 21:51:21 GMT

They say even a broken clock is right twice a day. In the same way, the Sun is “right” four times a year; the analemma shows how.

What time is it at noon? What a silly question! It's 12pm noon, at noon, right? ... Right?

Actually, not really.

Picture this: you take a photo of the Sun every single day at exactly the same time—let’s say 12:00pm noon local time—while standing in the exact same spot. Over the course of a year, the Sun won’t all line up in the same place – or even the middle of the sky. Instead, if you layer them together, you’ll see something that looks like a graceful figure-eight drawn across the sky. That sky-spanning doodle made by these layered,, timelapse, photos of the Sun is called the analemma.

Much like a broken clock that’s right twice a day, the analemma reveals that the Sun perfectly matches our clock time only four times a year. Let’s dive in to see why this phenomenon occurs, what it means, and why it’s such a fascinating part of our planet’s astronomical dance.

What Is the Analemma?

The analemma is the figure-eight path the Sun appears to trace in the sky when photographed at the same time of day over a full year. If you’ve ever seen an image of the Sun captured day after day in a beautiful loop, that’s the analemma in action.

Quick Facts:

• Shape: A figure-eight (∞) or a teardrop shape (depending on your latitude and how precisely the photos are taken).

• Why We Notice It: Because our clocks measure time differently than the “real” solar time, the Sun “arrives” a little early or late on most days, except on four specific ones when it’s exactly on time.

Why Does the Analemma Happen?

Two main ingredients give us this sky-spanning infinity sign:

1. Earth’s Tilt (Obliquity)

Our planet is tilted at about 23.5°. This tilt influences the height of the Sun in the sky throughout the year, causing the seasons. As Earth orbits, the Sun appears higher or lower, creating a vertical shift in the analemma.

2. Earth’s Elliptical Orbit

Earth doesn’t orbit the Sun in a perfect circle. Instead, we follow an ellipse, traveling faster when we’re closer to the Sun (around early January) and slower when we’re farther away (around early July). This causes a slight horizontal shift in the Sun’s position from day to day.

Combine these effects, and you get the figure-eight loop.

The “Four Times a Year” Phenomenon

The main reason we say the Sun is “right” four times a year has to do with something called the Equation of Time. Our convenient 24-hour clock is based on an average—known as mean solar time—but the actual Sun lags behind or runs ahead of that average on most days.

• When the Equation of Time is zero, real solar time matches our average clock time. That moment is when, if you look at your watch at noon, the Sun truly hits its local zenith (a.k.a. “solar noon”). This perfect alignment happens roughly four times each year (the exact dates shift slightly, but often fall near mid-April, mid-June, early September, and late December).

Observing the Analemma

You don’t need fancy equipment to appreciate the concept, though you do need patience (and safe solar viewing methods if you try to photograph it)!

1. Pick a Spot

Stand somewhere with a clear view of the sky where the Sun’s path won’t be blocked by tall buildings or trees.

2. Same Time, Same Place

Snap a photo (or record the Sun’s position) at the exact same time on as many clear days as you can over the year.

3. Compile Your Pictures

Overlay those images or plot the Sun’s position relative to a fixed landmark. You’ll start to see that telltale loop emerge.

Why It’s More Than Just a Cool Shape

Sure, the analemma is visually striking, but it also teaches us about Earth’s seasonal cycles, our timekeeping system, and just how elegantly our home planet moves through space. It’s a nod to the delicate interplay between rotation, revolution, and tilt—a cosmic waltz happening right above our heads.

Takeaway

So, back to that broken clock: it’s correct twice a day because chance lines up the clock’s hands with actual time in fleeting moments. In a similar way—but thanks to the Earth’s tilt and orbit, not mere chance—the Sun is “right” four times a year, making our noon alignment with the sky’s glowing star sync up perfectly. If you ever see a photo showing the Sun in a giant figure-eight, you’re looking at a year’s worth of mini-corrections, culminating in that graceful cosmic dance we call the analemma.

When someone asks, “What time is it at noon?” they’re hinting at a subtle truth: the Sun doesn’t always reach its highest point in the sky exactly at 12:00 by our clocks.

Due to Earth’s elliptical orbit and tilted axis, true solar noon—the moment the Sun stands at its local zenith—shifts from one day to the next. The analemma captures this shifting relationship by charting the Sun’s noontime position through the seasons, creating the familiar figure-eight shape.

It is, in essence, the visual answer to that deceptively simple question: “What time is it at noon?”

Stay curious, keep looking up, and remember: even if your watch is off by a few minutes, you’re in good company—our entire planet is running its own unique schedule in a grand astronomical ballet!

References

https://en.wikipedia.org/wiki/Analemma - lots of info here about the analemma

https://en.wikipedia.org/wiki/Equation_of_time - detail on the way "noon" slips around over the course of the year

https://ataridogdaze.com/science/heliotrak/heliotrak-visualizer.html - a cool tool for tracking the analemma and visualizing it yourself

https://www.analemma.com/intro.html - good intro with animations

Tristram Shandy's sky

Sat, 16 Dec 2023 22:27:32 GMT

The 18th-century English novel "The Life and Opinions of Tristram Shandy, Gentleman" (better known by its nickname Tristram Shandy - first published in 1759) reached its complete form in 1767. It was released in 9 volumes.

The Overthrow of Dr. Slop (Tristram Shandy) by Thomas Rowlandson is licensed under CC-CC0 1.0

Volume IV of Tristram Shandy has a passage describing the celestial positions of the Sun and planets on a specific date. The passage appears on Page 235 in the Penguin Edition 2003.

When I read that passage, I turned to Stellarium to check the (verifiable) accuracy of the statement. I wanted to "chart the planets" as described and I realized that I could use Stellarium to show the sky on that date.

Martin Luther's astrological birth chart

Here is the passage from the book - it is from the section where we are being introduced to the treatise on Noses by Hafen Slawkenbergius.

In the section the narrator discusses the disagreements over whether an astrological charting of the planets at the date of his birth tells of the fate of the soul for one, Martin Luther:

Portrait of Martin Luther by Johann Michael Püchler is licensed under CC-CC0 1.0

"...determining the point of Martin Luther's damnation.

The Popish doctors had undertaken to demonstrate a priori ; that from the necessary influence of the planets on the twenty-second day of October 1483 ---- when the moon was in the twelfth house -- Jupiter, Mars, and Venus in the third, the Sun, Saturn, and Mercury all got together in the fourth -- that he must in course, and unavoidably be a damn'd man -- and that his doctrines, by a direct corollary, must be damn'd doctrines too."

Martin Luther's Birthdate for Stellarium

So, since the date was laid out so precisely, I typed that date into Stellarium and looked at exactly where the Sun and planets were described to be.

The Year 1483,

The Month, October,

The Day, 22.

The sky, was described reasonably accurately. You see the old Moon near Leo, the Sun in Libra (which would have been considered Scorpio in Sterne's day), Jupiter, Venus, Mars, and Saturn, all lined up in groups as described in the passage.

Here is the image that Stellarium produced for that date:

Image of Stellarium sky showing the birthdate (Oct. 22, 1483) of Martin Luther as indicated in the novel Tristram Shandy
Image composition and overlay by Daniel Cummings © 2023

EDIT: Updated based on Martin Luther's "new" birthday date.

Since the positions of the sky objects in the first chart were only close to those described in the passage, I moved the birthdate to Martin Luther's "official" birthday on November 10th, 1483 to see the difference. And, it works better with this new date:

Second Image of Stellarium sky showing the "new" birthdate (Nov. 10, 1483) of Martin Luther as indicated in the novel Tristram Shandy
Image composition and overlay by Daniel Cummings © 2023

The difference in date might be an error in Laurence Sterne's text, or it might be a difference in calendaring systems. The Gregorian calendar was not adopted Britain until 1752.

Oddly, (and the case may be made here that the Sterne date is an error) the difference between the date in the book and the date of Luther's birthday amounts to 19 days, while the day change between the old (Julian) and new calendar (the Gregorian, adopted between 1582 and the 20th century) is 11 days. [Editor's note: The shrug emoji was made for just this situation. 🤷‍♂️]

Astronomy is not astrology.

Please note: in the past, astrology and astronomy were one discipline, and the practitioner of astrology was often the court astronomer. These practices have now separated and astronomy is a full-fledged science while astrology is a charming, diverting pastime.

I hope you enjoyed the journey.

I highly recommend Tristram Shandy and Stellarium.

In each, on their own, there is a powerful genius.

Get closer to the Moon without leaving the Earth

Sun, 11 Dec 2022 17:15:58 GMT

Astronomy Koan by Daniel Cummings

How close can I get to the Moon while still staying on the Earth's surface?

I frame this as a sort of astronomy poem I call an Astronomy Koan. These are short sayings that contain astronomy puzzles. The answers to these puzzles carry insights into physical astronomy concepts.

Guy Ottewell has posted an article at UniversalWorkshop.com about getting close to the Moon. https://www.universalworkshop.com/2022/12/11/how-to-touch-the-moon-almost/

"I am close the the Moon but not as close as I can be." This Astronomy Koan invites the reader to consider all of the ways which an Earth-bound observer might get as close to the Moon as humanly possible - without leaving the surface of the Earth.

The Earth and Moon are moving, I am moving

The Moon and the Earth are two oblate spheroids interacting in complex ways.

The Earth-bound observer is able to move around on the surface of the Earth while we calculate the "closest" point of the Moon to be the surface point that is closest to a surface point on Earth.

The goal of the Earth-bound observer is to find the location and time where they will be physically closest to the Moon.

Motions of the Moon that bring the Moon closer and further to your "closest personal point"

Daily apparent revolution - every 24h 50m wherever we are on the Earth surface, the Moon transits (crosses the meridian) and reaches the "closest personal point" at that time.
The apsides of the Moon's orbit - the Moon's orbit is slightly elliptical and has an apogee (furthest point from Earth) and a perigee (closest point to Earth). If a perigee coincides with a Moon transit, this brings the Moon even closer to the surface of the Earth. Approximately 357000km (perigee) and 406000km (apogee)
The inclined orbital track of the Moon. Close to the ecliptic, but an additional 5 degrees offset, this gives the Moon an opportunity to be closest to people located on the surface of the Earth who are slightly north (up to 5.14 degrees) of the Tropic of Cancer and south of the Tropic of Capricorn.
The Moon's orbit is slowly moving away from the Earth (by 3.8cm per year, about 38km in 1million years) - so the longer you wait, the further away it will be!
Surface of the Moon orientation toward my location - East-west libration moves the "orientation" of the Moon as it relates to the Earth
The surface of the Moon has crater walls and valleys. The closest point would be at the height of a crater wall or central peak. Hipparchus crater or Triesnecker crater seem like likely candidates because they are "central", but this is beyond my understanding of the topology of the Moon surface and how it might interact with the orientation changes caused by libration, nutation, and the inclined orbit.

My motions on the Earth that can get me closer to the Moon

The transit can be made closer by moving closer on the surface of the Earth to the current declination of the Moon. Generally speaking, that involves going toward the equator, but it get complicated by the fact that the orbit is inclined to the equator and ecliptic.
The transit can be made closer by going to a higher elevation
The transit can be made closer by going to the top of a mountain close to the equator (Mt. Chimborazo as opposed to a tall mountain like Everest that is not near the Equator)

The "ideal" situation that would bring a human on the surface of the Earth as close as can be to the Moon would be

Stand at the top of Mt. Chimborazo, at the moment of Moon transit, at the exact orbital perigee, with Hipparchus crater wall oriented toward Mt. Chimborazo, as soon as possible!

Summary

We looked at all of the ways that the Earth and Moon approach and recede from each other. The goal is to understand more directly when I am close to the Moon and observe the motions that change that distance.

Please let me know if I have missed anything here! Add in comments below.

References:

NASA Moon page: https://svs.gsfc.nasa.gov/5048 - has "an animated diagram of the subsolar and sub-Earth points for 2023" Indicates the general sweep of the "closest Moon-Earth point" as it traces out irregular shapes on the surface of the Moon.

NOAA answers a question about the "tallest" mountain, Mt. Chimborazo: https://oceanservice.noaa.gov/facts/highestpoint.html

ASC page with information about the various motions of the Moon: https://www.rasc.ca/motions-moon

Wikipedia Orbit of the Moon article: https://en.wikipedia.org/wiki/Orbit_of_the_Moon

Wikipedia Lunar Distance (measure the distance from the center of the Earth to the center of the Moon): https://en.wikipedia.org/wiki/Lunar_distance_(astronomy)

Moon orbit distance growing: https://astronomy.com/magazine/ask-astro/2022/08/ask-astro-how-quickly-is-the-moon-moving-away-from-earth

Quora Answer that mentions Mt. Chimborazo: https://www.quora.com/Where-on-Earth-is-the-closest-point-to-the-Moon

Comments

John Cummings - December 11, 2022 at 5:38 PM

Interesting but a bit too esoteric for me

Daniel Cummings - December 11, 2022 at 7:02 PM

Thanks for the note! Basically, you are as close as you can be to the Moon once per day when it is directly overhead (as we rotate underneath it) and then you can get even closer when the Moon is at perigee (closest point in its orbit around the Earth). The other motions are interesting but have less of an effect on how close you are to the Moon at any given time.

GPS uses Quasars

Fri, 07 Jan 2022 21:35:00 GMT

GPS uses Quasars to work

GPS satellite in low Earth orbit. Credit: NASA artist's impressionThe Global Positioning System (GPS) is precise. That precision originates in a mind-blowing place! GPS signals tell billions of people where they are each day. GPS helps pilots land planes and captains steer ships. GPS signals stamp locations onto millions of photos per minute. GPS gives you driving directions. But, where does GPS get its own GPS?

The GPS for GPS

How does GPS know where a GPS satellite is? The GPS system has to know where the GPS satellites are so it can tell the satellite. The base GPS system can't just ask GPS, because GPS is supposed to provide the authoritative positioning data. It would set up a catch-22 situation. The answer is that, ultimately, quasars anchor the GPS system.

What is a quasar?

Artist's impression of a Quasar with high energy jets. NASA image. GPS uses quasars. Yes, quasars... These are black holes that eat matter and spew jets of deadly radio energy. In more scientific terms, a quasar is a black hole in another galaxy that emits a strong radio signal. Quasars make good anchor points. The stars in our own galaxy are constantly moving. But, quasars are so far away that they stay still. Also, even though they are invisible to the human eye, they are such strong radio sources that astronomers identify and track them with radio telescopes. They use these locations to get a foundational "place" in space. GPS signals can be based on this foundational place. The location of this "zero point" is set by in the positions of 212 quasars mapped by a fleet of radio telescopes. GPS uses these quasars to set its origin. It's the GPS for GPS.

GPS uses 212 Quasars

The 212 GPS Quasars. Astronomers know these as Extragalactic Radio Sources. They are the foundation for accurate GPS positioning. Quasar projection map fusion by Daniel Cummings, quasar locations courtesy NASA. A flattened version of the Quasar GPS map. The image above shows quasars plotted as Earth surface locations (as mapped on the celestial sphere). This is a map of quasars and their locations on the celestial sphere. If you want to imagine them in 3D, you can imagine straight lines or threads connected from every part of Earth. These lines poke straight out like 212 dry spaghetti strands stuck into a foam ball. Each strand points at an individual quasar.

Quasars do not move; they are far away and not visible

Imagine viewing a pencil lead edge on - it is super small. Now imagine taking it to the other end of a soccer field - even smaller, right? Now imagine that pencil lead was in San Diego and you viewed it from a location across the USA thousands of miles away in an east coast city like Washington DC. This is how precise the measurements of the quasar positions are. Astronomers who spend most of their time measuring things or building tools to measure things are called Astrometrists (astronomers who focus on the astronomical measurements). It sounds a lot like Optometrist to me. The main reason that Astrometrists chose to have GPS use quasars is because they are so far away that they do not move. In fact, all of the 212 quasars used to create the zero point are in different galaxies. The trouble with quasars is they are not visible. They have strong radio frequencies, but they are completely invisible - in fact, they are so faint, the Hubble Space telescope can't even see them.

Do GPS satellites "talk" directly with the quasars?

GPS satellites do not talk directly to quasars. GPS satellites only "talk" to ground stations to get the time and their orbital position. Then they broadcast that data in a repeating pattern that GPS receivers can understand. But, the ground stations have to know their position. They use a "reference frame" to figure out their own position. This is the "mother of all coordinates" for astronomers. The Earth centric "reference frame" is called the Geocentric Celestial Reference System (GCRS). The GCRS looks in turn at the International Celestial Reference System (ICRS) for its position. And the ICRS looks at quasars.

The sequence of position "givers" from GPS unit to quasar.

GPS unit -> GPS Satellite -> GPS Ground Station -> GCRS -> ICRS -> Quasar Astrometrists create a "reference frame" for GPS that uses 212 quasars. The reference frame creates an origin point based on the positions of those 212 objects. All astronomy and space positioning systems use that point as zero, zero; including GPS. Everyone on Earth agrees to use this system.

Summary

Quasars are black holes in remote galaxies. Astronomers measure the positions of quasars to an astounding degree of accuracy: 40 microarcseconds. GPS uses quasars as anchor points to get the original position. Every other GPS position is based on that original position.

Fun Facts

GPS uses quasars. The official GPS time clock start date is January 6, 1980. This is kind of like GPS Birthday. We should celebrate "GPS Day" on January 6th each year!

References

International Celestial Reference Frame (Wikipedia) — Mentions how "212 extragalactic sources (mostly quasars)" are used as a reference frame. All clocks are set based on this frame, therefore all GPS devices are "anchored" to quasars.
NASA: ICRF2 — General audience description of GPS relationship to quasars with quotes from Chopo Ma from Goddard Space Flight Center.
Deep Space Objects Guide Earth's GPS System (Space.com) — Another general audience introduction with similar quotes from Chopo Ma from Goddard Space Flight Center.
NASA Space Map Uses Quasars to Guide GPS Satnavs (The Telegraph) — A third article quoting Dr. Chopo Ma. This was big news in November 2009 but nobody has written on it much since then. Includes a nice image of the quasar "locations" as well as an artist's impression.
ICRF Research Paper (arXiv PDF) — More detailed paper direct from the researchers compiling and cleaning the data.
Making the ICRF More Precise (PDF) — 2017 writings on making the ICRF even more precise.
Astrometry Overview (University of Arizona PDF) — Astrometry overview from The University of Arizona.
Beacons in the Sky Help Monitor Earth's Orientation in Space (NASA) — Related article discovered after the post was written.

Remember the planets

Mon, 06 Sep 2021 09:40:00 GMT

The eight (8) planets in order from the Sun.
NOTE: the sizes are to scale and the ordering is correct, but the distances are not to scale.

Here are the planet names in order of distance from the Sun.

Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune

You can use this mnemonic (memory helper) to learn it.

My Very Educated Mother Just Served Us Nachos.

Learn how to remember the planets and the names and order.

References

https://en.m.wikipedia.org/wiki/Planetary_mnemonic

Comments

Pat - September 6, 2021 at 2:06 PM

Every good boy does fine? Did your earnest mother teach you that?

Daniel Cummings - September 6, 2021 at 2:11 PM

Hah! I learned it from my Science teacher in middle school. :-)

Countries in the Sky

Mon, 30 Aug 2021 08:30:00 GMT

A spot on Earth is a spot in the sky.

Every "spot" on Earth has a corresponding "spot" in the sky. For instance, on the spot where you are now, directly overhead, is the zenith. There is only one zenith where you stand. No two spots share the same zenith. Every spot on a sphere "points to" a different location in the sky. Nobody shares your zenith.

Your Zenith is Unique

Imagine the boundary of your country as a set of these spots. These locations can be projected onto the celestial sphere. Projecting shapes of countries onto the sky can help you really "see" how large or small a country is. Seeing countries from the inside out helps to understand the shape of the Earth as a sphere.

The ZenithMap is a tool I created to help you visualize your country in the sky.

That Star is Someone's "First Star I See Tonight."

When you see a star rising you are actually seeing a star that someone 6 timezones east of you sees directly overhead.

Sirius rises just before dawn (heliacal rising) in mid August (at latitude 40˚N). It rises earlier and earlier each day until by November it is rising at midnight. When people on the east coast of the USA see Sirius rising, people in Western Europe see the same star Sirius high in the sky at the meridian.

Do Stars Move?

Mon, 23 Aug 2021 08:33:00 GMT

Dalle-2 Generated this image of a figure standing, wondering at the cosmos. Prompt: “gentle, happy 8 year old child, standing in a sunset forest, looking through a small, glass-covered hole in the earth that has stars deep inside, digital art, unsaturated colors” - Credit: Daniel Cummings

Heliacal rising.

Sidereal time.

Take a picture of the stars before the dawn every day.

Just before dawn, while the sky is still dark, and the stars are still out.

Tomorrow, the same thing, just before dawn, while the Earth still blocks the Sun.

there are stars in the daytime sky

Thu, 19 Aug 2021 21:28:58 GMT

to the west of the noonday sun are the stars that were up when the day had just begun.

to the east of the sun are the stars that will come out when this very day is very nearly done.

- daniel cummings 2021

Comments

Patricia Cummings - August 21, 2021 at 12:45 PM

I always wished that I could see the stars during daylight.

Daniel Cummings - August 22, 2021 at 1:06 PM

They are always there. During a full solar eclipse you can see the stars appear in the daytime sky.

How Fast is the Earth Moving? - A Quiz

Wed, 24 Feb 2021 07:05:00 GMT

A family views the visible orbit path of the earth.

"How fast?" means "What is our velocity?" Velocity is a speed combined with a direction. We can figure out our speed and our direction on the Earth by looking at these 6 motions and directions...

But, before you read these, try to think of the 6 different motions that the Earth has.

Just putting some space in here to give you time to think about the Quiz.

_________________________________________________

The answer:

Rotation of Earth (cycle) - 0.5 km/sec
Orbit around Sun (cycle) - 30 km/sec
Solar System through Galaxy (cycle) - 200 km/sec
Milky Way Galaxy moving toward Andromeda within the Local Group (non-cyclical toward Andromeda)- 109 km/sec
Local Group motion inside Virgo Supercluster (non-cyclical toward "overdense" regions) - 300 km/sec
Cosmic Void repulsion (non-cyclical) - 600 km/sec

Earth's Overall motion = 368 km/sec +/- 30 km/sec depending on season

Our overall direction of motion? The Cosmic Microwave Background (CMB) tells us generally which direction we are moving in: towards the "overdense" regions of the Cosmic Void.

References

Thanks for Ethan Seigel for gathering all the relevant data points for this quiz.

https://www.forbes.com/sites/startswithabang/2017/06/16/how-does-earth-move-through-space-now-we-know-on-every-scale/#4a1dd5d4861f

Comments

John Cummings - February 24, 2021 at 8:06 AM

Where are the questions? I just see the answers...

Daniel Cummings - February 25, 2021 at 12:00 PM

Hi! The quiz is just to try to imagine all of the Earth's motions in space. Most readers will easily come up with rotation, revolution around the Sun, the motion of the Sun, and even the motion of the Galaxy... thanks for visiting!

Super Simple Earth Model

Sun, 21 Feb 2021 07:27:00 GMT

Super Simple Earth Model

Physical Astronomy by Daniel Cummings

Stand outside on a sunny day or in a room with only one light. If you are inside the light should be at eye level when you are standing up. This will be your Sun.

Stand up, make sure there is space around you - things might get messy if you start spinning like the earth and there are things to bump into.

Turn to the left and begin a slow leftward spin. This is the direction that the Earth rotates (as "seen" from above the north pole).

Your head is like the earth. Your eyes are like two different people on the surface of the earth. They are looking straight out from the earth toward the sun.

As you spin in your leftward rotation, wink your left eye shut. Observe how your left eye can see the light before your right eye. This is like the east and west coasts of the USA. The east coast is a few hours ahead. Observe how when you continue to spin and your eyes turn away from the light source it is like night.

Spin a few times more to feel yourself as the Earth model. 29-31 spins makes a month. 365 spins makes a year. Multiply your age in years by 400 and that's about how many days you've been riding on the earth - give or take a few hundred.

Galileo's Middle Finger

Wed, 17 Feb 2021 21:59:00 GMT

Galileo's Middle Finger

In 1737, Galileo's body was moved from one burial place to another. During the move several of his fingers and a tooth were removed from the body. Gruesome as it seems, this was a common treatment for the bodily remains of famous people.

One of the fingers - his middle one - eventually ended up in a museum in Florence where it sits (standing straight up) on a marble plinth under a glass jar.

Galilieo's Middle Finger. From Wikipedia - Photo by User Saliko

Galileo's science won the day, eventually, and after much suffering. However, thanks to this wonderful museum display, Galileo also got the final word in his epic battle with the powers of the Roman Inquisition - he's giving them the finger - until eternity.

References:

Galileo Galilei wikipedia page

Constellations of the Zodiac in Order

Mon, 20 Jul 2020 09:24:39 GMT

Learning the Zodiac constellations in order is a great way to get familiar with the ecliptic and the celestial sphere. The Zodiac is not just for astrology - astronomers use the constellations of the Zodiac to name 13 regions of the sky.

Zodiac Constellations zoomed in on Ophiuchus - the "13th" Zodiac Constellation between Sagittarius and Scorpio. The constellation borders (marked red) show how astronomers divide up the sky into named regions.

Zodiac Constellations List

These are the Zodiac constellations in the correct order from Aries to Pisces.

#	Mnemonic	Name	Description	Emojis
1	A	Aries	Ram	♈ 🐏
2	Time	Taurus	Bull	♉ 🐄
3	Gone,	Gemini	Twins	♊ 👯‍♂️
4	Cowboys	Cancer	Crab	♋ 🦀
5	Loved	Leo	Lion	♌ 🦁
6	Viewing	Virgo	Virgin	♍ 👰
7	Little	Libra	Scales	♎ ⚖️
8	Stars,	Scorpio	Scorpion	♏ 🦂
9	(Oh)	Ophiuchus	Snake-wrestler	⛎ 🐍🤼‍♂️
10	So	Sagittarius	Archer	♐ 🏹
11	Cold	Capricorn	Goat-Fish	♑ 🐐🐠
12	And	Aquarius	Water-bearer	♒ 🚰
13	Pretty	Pisces	Fish	♓ 🐟

Memorize the Constellations of the Zodiac in order

This mnemonic (memory device) can help you remember the correct order of the constellations of the Zodiac. This is the best way to memorize the order of the constellations of the Zodiac. It starts with Aries and ends with Pisces.

This sentence is good - it's a bit romantic and easy to say.

“A time gone, cowboys loved viewing little stars, (oh) so cold and pretty.”

- Terry Johnson (original - oh added by DC)

Another phrasing you might like.

"All the great constellations look very lovely; shining, (orderly) stars creating animal patterns.”

- Alex Davo (original - orderly added by DC)

Why does the Zodiac constellations list start with Aries?

When astrology was invented it was the same activity as astronomy - observing and cataloging sky objects and their locations) but over the years the two practices have become very different. Astrology is now concerned with how the movement of the skies affects humans while astronomy has become a science. Scientists build knowledge to make predictions about physical events.

During early astrology/astronomy times, the most important thing about the study of the stars was to know where the Sun, Moon, planets, and other solar system objects were located in relation to the steady, orderly background of stars.

Why does the order of the Zodiac constellations read right to left?

The Sun moving "through" Aries into Taurus over a month. Each frame of the animation is about 3 days.

The Sun, Moon, and planets seem to move "through" these 13 constellations in order through the year. Starting with Aries, let's follow the movement of the Sun against the backdrop of the steady stars. The next constellation that the Sun "moves into" is Taurus. Taurus is to the east (left) of Aries! The Sun appears to move into the next Zodiac constellation about once a month.

We know that the Sun is not moving - that it only appears to move through the sky - and that it is the Earth's orbital motion that is creating this apparent movement.

Why did we add Ophiuchus to the original 12 Zodiac constellations?

Ophiuchus is a constellation, not an astrology "sign." However, it is an official constellation that intersects the ecliptic. So, while astrologers do not consider this a Zodiac sign, astronomers include it because the constellation is located on the ecliptic.

The Ecliptic is a path in the sky that solar system objects follow

The solar system objects move generally west-to-east in a small band of the sky - this band of sky is called the ecliptic. All the Zodiac constellations are "on" the ecliptic and all the Sun, Moon, planets and other solar system objects move along the ecliptic over time.

There is another line in the sky called the celestial equator that is an imaginary line the rises from the equator of the Earth. The celestial equator and the ecliptic intersect at a "location" in the sky.

Right now in 2020 that intersection location is "in" the constellation Pisces.

The thin, diagonal line that connects the Zodiac constellations is called the ecliptic. This image shows the ecliptic intersecting with the celestial equator.

However, when astrology was created this intersection point was "in" the constellation Aries.

This image shows the intersection of the ecliptic with the celestial equator in the year 100 BCE.

This was known as the "First Point of Aries." Astronomer Guy Ottewell writes about this imaginary point in the sky on his website UniversalWorkshop.

Summary

You can learn the order of the Zodiac constellations by using the mnemonic device shown in this article. There is a pathway in the sky that the solar system objects seem to follow. It is called the ecliptic. The Zodiac constellations are the 13 constellations lined up in the sky "on" this imaginary line.

The order of the Zodiac constellations is made because of the way the Sun, Moon, and planets seem to move east-to-west past these constellations in order during the year.

We start the Zodiac names list with Aries because the Zodiac constellations were first named thousands of years ago. At this time, the ecliptic intersected the celestial equator "in" the constellation Aries.

Seeing The Zodiac - A Stellarium Script Tutorial

Wed, 08 Jul 2020 15:20:00 GMT

🔭 I am a Live Planetarium Presenter - "Planetariumist" - at the Fresh Air Fund's Gustafson Planetarium at Sharpe Reservation in Fishkill, NY. We Planetariumists are learning to use Stellarium scripts. This article will teach you how to use a Stellarium script to quickly load the art images for the 13 Zodiac constellations:

Aries Taurus Gemini Cancer Leo Virgo Libra Scorpius (Ophiuchus) Sagittarius Capricornus Aquarius Pisces

A selfie from inside the Gustaffson Planetarium at the Fresh Air Fund Sharpe Reservation in Fishkill, NY

Online Camp programs for Astronomy Education

Like every other camp program during COVID-19 times we have had to move the live shows to an online format. In our case we are doing zoom astronomy presentations for the campers. It's been a great experience to learn how to do quick and entertaining astronomy shows online and I wanted to share a few tips to make better astronomy online presentations.

Stellarium Scripts for Astronomy Zooms

I want to make Stellarium really work for online presentations like zoom astronomy outreach, so I figured out how to write scripts to control it. To get started, I just copy-pasted and modified an existing script that did something like what I wanted it to do.

Zodiac Art in Stellarium showing the Sun "in" Gemni on July 8, 2020 from Flushing Meadows, Queens, NY

Stellarium scripts help you do the tedious set up and configuration steps. There is no need to open windows and drag and click around while your audience waits!

Below is a Stellarium script I adapted from the original zodiac.ssc that highlights the Zodiac constellations with art, names, and boundaries and it shows the ecliptic. The original script that comes with Stellarium had some features that I didn't need so I copy-pasted a new one. My new script simply shows the Zodiac constellation art in just 5 seconds. This would take at least a minute to complete by hand! So, this is a great timesaver if you are presenting to a group via online zoom conference.

Stellarium Script - show Zodiac Art, Boundaries, Ecliptic

You can click here to download the script as a zip file. Unzip this download and you will have the .ssc file in your downloads area. Or you can just copy-paste the text below and create your own script file.

Here is a quick gif animation of what the presentation screen looks like while loading the Zodiac Art Boundaries and Ecliptic in the Stellarium Astronomy Zoom presentation.

An animated GIF showing the end result when you install the new Zodiac script.

Using the New Zodiac Art Boundaries and Ecliptic Script - Tutorial

Installing scripts is as easy as creating a text file with this script and placing the "script_name_here.ssc" file in the scripts directory. In this case, name your script file: zodiac_art_boundaries_ecliptic.ssc

After this "Zodiac Constellation Art Boundaries Ecliptic" script is installed in your Stellarium you'll be able to get to it and run it from the Scripts tab of the Configuration window.

Instructions to Install a Stellarium Script

On Windows: You have to find the Stellarium User Data directory and inside that will be the scripts directory. (NOTE: I don't have a windows machine so there is probably more information required here. Please add a comment to this post if you discover that I have left something out.)

C:\Users\YOURUSERNAME\AppData\Roaming\Stellarium

If it doesn't already exist, create a new folder named "scripts" - leave out the quotes.

Windows file explorer view of where to place the script.

Move your downloaded or created .ssc file to this folder.

On Mac: you have to control-click (hold the control button and click the mouse) the Stellarium.app in the Applications directory and choose "Show Package Contents"

You then navigate to the scripts directory in: Contents > Resources > scripts.

Place the script file in the scripts directory. Quit and re-open Stellarium and the script will be in the list of scripts in the Scripts tab of the Configuration window (see graphic above earlier in the article).

If you want to be fancy and use the included key command ...

Using Stellarium Script Trigger "Sequence" commands

This custom Stellarium Script comes with a key command I programmed which is a "sequence command" - two steps. First do Control/Command-D, then release those keys and type the letter z key.

Try out the script and let me know what you think by typing in the comments field below! Also, if you want me to write a custom script to speed up your Stellarium presentations I'd love to help out - give me your suggestions.

Stellarium is a potent tool to help you see the sky

I have written few other articles about using Stellarium.

Stellarium - a gift to Humanity - Learn to see the sky

Time Travel with Stellarium - See the sky in timelapse!

Stellarium and the Humanity Star - a short-lived satellite

See the Analemma with Stellarium

About the author of this Stellarium script tutorial

🔭 Hello! I am Daniel Cummings - the creator of the fun and fashionable science clothing The Moon Hat (Forbes named it Best Science Gift in 2018). I am also one of the Live Planetarium Presenters - "Planetariumists" - at the Fresh Air Fund's Gustafson Planetarium at Sharpe Reservation in Fishkill, NY. I've written about and presented astronomy and space topics since 2008. Sign up on my email list to hear more about astronomy and space.

Comments

Pingback: […] west-to-east in a small band of the sky – this band of sky is called the ecliptic. All the Zodiac constellations are “on” the ecliptic and all the Sun, Moon, planets and other solar system objects move along the ecliptic over […]

Galaxy Horizon - 4/20 at Midnight

Sun, 19 Apr 2020 22:28:23 GMT

On April 20th (4/20) at midnight Earth's horizon (in northern latitudes) lines up perfectly with the plane of the entire Milky Way galaxy. The galaxy "wraps around" our view of the sky and we can see into and through the plane of the galaxy.

The Milky Way galaxy lines up perfectly with your local horizon view on April 20th (4/20) at midnight each year.

At this moment when you look out around you at the horizon, you are looking into the plane of the Milky Way galaxy.

How to See the Milky Way Galaxy Plane

Look southward (and a little bit east) and you are looking toward the center of the galaxy. Look northward (and a little bit west) and you are looking toward the outer edges of the galaxy.

Why does the galaxy line up with the horizon?

Each year on 4/20 the galaxy lines up with the horizon - an "event" I call the Galaxy Horizon. In fact, this "event" occurs every day! It's just an interesting coincidence that the alignment happens on 4/20 at midnight. Each day the galaxy lines up again with the horizon but it happens 4 minutes earlier.

Earth Map in the Sky

Mon, 02 Dec 2019 20:00:03 GMT

Earth Map in the Sky - Landforms as Constellations

Learn how to see the map of Earth in the starry sky.

Stars help us find our way. Stars are like a giant map in the sky that tells us where we are on the surface of the Earth. Sailors use them as a "map" to navigate the world. For thousands of years, the stars were stationary markers of latitude and longitude.

We are going to learn to map something new onto the sky: locations on the Earth! We can create an exciting new set of "constellations" out of the shapes of the continents on the Earth.

We live on a sphere so we can see half of the sky (a hemisphere) at any one moment. It's easy to imagine half the Earth mapped onto half the sky. Keep reading to learn how.

A new way to experience life on a sphere. It's an Earth map projected onto the starry sky. Image created by: Daniel Cummings

Zenith Stars

Wherever you are on the Earth, when you look straight up (toward your zenith), you might see one star, but there are a bunch of other stars within view. All of the stars you see in the sky are directly overhead some other place on the Earth. Every place on Earth has their own set of stars directly overhead - their "zenith stars."

Look up at any star in the night sky; that star is directly over some place on Earth. There are hundreds of "faraway zeniths" up there.

World Zeniths - See the Map of the Earth in the Sky

Every star maps to a location on Earth and every location on Earth maps to a star.

If you live in the western hemisphere, you can learn to look up and "see" the land borders of the North American and South American continents visible, projected into the sky like a giant painting on a curved ceiling. You can learn to see even more landforms in the sky - you can learn to see the entire western half of the Earth projected in the sky.

Visualize Countries in the Sky

We can learn to see country outlines in the sky. The key is to imagine yourself at the center of the Earth looking out into space "through" a translucent Earth surface.

Here is a good way to visualize these countries-in-the-sky even when you are on the surface. Imagine that you can look up and see your location at the zenith.

When I do this, I see southern New York state, Long Island jutting out into the water like a long pier, and the wide Hudson River emptying past New York City. Eastward is the dark expanse of the Atlantic Ocean and low on the eastern horizon are the countries of Europe and West Africa.

Westward in the sky, I can see the outline of the west coast of the US. Then, there is a big blank space of the Pacific Ocean and a spot near the western horizon that is Hawaii.

The Map of the Earth in the Sky is Reversed

Map of Earth landforms as they map to the starry sky. Map is reversed because it is projected into the sky. The places named at the cardinal directions (N, E, S, W) are the locations where New York horizon stars are zenith stars. Image created by: Daniel Cummings

There is one odd thing about the map as you see it in the sky... it's reversed - as if seen in a mirror! This happens because we project the map lines outward into space toward the stars. When we look at the map this way it's as if we are "inside" the Earth looking outward.

The map of the USA covers about 58˚ of sky from east-to-west. 58˚ is about 2x pinky-to-thumb (spread out all your fingers of both hands and touch thumbs). Your left pinky tip should be on your zenith. If you are in New York or somewhere on the east coast, the right pinky tip will indicate the approximate western edge of the USA.

Physical Astronomy - Stars Map to Places on Earth

Physical Astronomy Activity Instructions to learn to see the Map of the Earth in the Sky. Faraway Zenith stars help us visualize what it is like to live on the surface of a sphere. Image created by: Daniel Cummings

Learn to see the zenith map in your sky using this Physical Astronomy technique.

Exercise 1: face south and point high in the sky.

Face south. Then, reach both hands straight up over your head and point above your head with both pointer fingers. You are pointing at your zenith. Now, bring both arms down until they are pointing one due east and one due west. You are pointing at two points in the sky that are zeniths for someone else.

When I do this exercise in New York, my left hand (the eastern) points at a spot in the starry sky that is the zenith star for someone in the country of Nigeria in West Africa. This is a location on the globe that is 6 time zones east. My right hand (the western) points at a spot in the sky that is the zenith for someone in the island state of Hawaii in the middle of the Pacific Ocean. This location is 6 time zones west of New York.

So, when I look at the eastern horizon sky I am looking at the starry sky that is already directly above a place 6 time zones ahead of me. I am looking at someone else's zenith stars.

Exercise 2: Repeat exercise 1. But this time, face east.

Face east, point up. Now, bring your arms down and point toward the north and the south directions. This time your right hand points south and your left hand points north. Your right hand points at a spot in the sky that is over the city of Cuzco, Peru (the closest city to Machu Pichu) and your left hand points to sky that is over Yekaterinburg, Russia - the 4th largest city in Russia.

Secret! You Can See a Star That Another Person Can't

If you do this physical astronomy exercise right after sunset, the eastern and southern zenith locations are in night, but the western and northern sky points are over Earth locations that still have daytime.

This means that you can see the star that is at their zenith, but they cannot see that star. For example, Seattle still has 3 hours of sunlight left in their day so stars are invisible behind blue sky. The city of Yekaterinburg is on the opposite side of the world and just after sunset in New York it faces the Sun and has a bright daytime sky!

We are on the night time side of the Earth and we can see the current zenith stars of Seattle and Yekaterinburg - but people who live in these cities cannot see them! They have to wait to rotate to the night time side of the Earth to see stars.

The Math - How High Up is the Zenith Map?

Guy Ottewell's illustration from Astronomical Companion (page 8). This schematic shows how we experience the celestial sphere - the array of stars in the sky. It shows zenith, cardinal direction points, the meridian, the celestial equator, the ecliptic, and the viewer - you, in England - sitting on the globe at latitude 40˚ north, looking up at the sky. Credit: © 2016 Guy Ottewell - UniversalWorkshop.com - used with permission.

Project an imaginary map of the Earth into the sky. The map has to be the correct size so that when it is viewed from a distance it "covers" the same distances.

If a map is too close, it is just the same size as the territory. So, we have to choose the correct distance to project the zeniths. As the zenith map "projector screen" moves away from the Earth we see more of the borders of the Earth. But, at some point the distance of the map corresponds exactly to the faraway zeniths.

Our question is: "How far away from the Earth do you have to be so the landforms (like the continents) have an angular diameter that is equivalent to their "actual size" in the sky?" How far away does our imaginary zenith map USA (about 3000 miles wide) image have to be to cover 58 degrees of arc in the sky?

To answer this we need math.

The Zenith Map Distance from Earth

Earth map showing close up of Algol passing over New York City while Gorgonea Tertia approaches Washington DC. Almach is the Zenith Star somewhere near Chicago, IL. The Earth's rotational speed at this latitude makes the stars appear to travel a little bit faster than the speed of sound. They will be Zenith Stars for a location about 800 miles west in 1 hour. Image created by: Daniel Cummings

The Earth is approximately 24,901 miles in circumference at the equator. If we can see half the sky from any point on the Earth, then we can "see" half the Earth projected onto the sky by the zenith map. That means that for 180˚ of sky we can "see" about 12,450 miles of the Earth's surface projected into space. 12,450/180 = 69 miles. When 1 degree of arc spans 69 equatorial miles the image is "at" the correct distance.

1 Degree of Sky equals 69 Miles

So, at the equator every degree of sky covers about 69 miles in every direction. As you go towards the poles the longitude degrees (east and west) cover less and less zenith map distance, but the latitude degrees (north and south) always stretch 69 miles. Every 15˚ of sky equals about 1035 (69*15) miles.

The distance between your pointer finger and your pinky (when you hold your arm and hand stretched out in front of you) is 15˚ - so you are measuring about 1035 miles on Earth with that sky measurement. One pinky width is equal to 1˚, which is 69 miles of zenith map!

The Math - Inverse Tangent and Angular Diameter

There is a simple calculation that helps us determine how far away something needs to be to fill just 1˚ of the sky. Here we use just a tiny drop of trigonometry to discover the "tangent of 1 degree."

The tangent of 1˚ is 0.017455. The inverse of something is when you divide 1 by the number you want to invert. So, the inverse of 0.017455 (1/0.017455) is 57.29. The inverse of the tangent of 1˚ helps us figure out the distance something has to be to appear to be 1 degree angular diameter.

This page explains how to calculate distance from a known angular size. "When an object's distance is 57.29 times its size, it has an angular size of 1 degree."

So, 57.29 * 69 miles = 3,953 miles away! This is how far away the "map" has to be to show you your hemisphere of the Earth map. 3,953 miles is higher than low Earth orbit (LEO) satellites (lower than 1200 miles); it's closer than geosynchronous satellites (at about 23,000 miles); and it's about 1/60 the way to the Moon.

So, imagine that the Earth map is projected onto a screen - an imaginary celestial sphere, shell-shaped - that is quite close to the Earth and encircles us. It shows us our Earthen landforms and the oceans beside, superimposed in the sky.

Summary

We live on a sphere. When we look at out night sky we are able to see stars low on our horizon that are visible directly above someone else - one-quarter the way around the around the world in all directions.

If you live within 6 time zones of someone that means that you share some "simultaneous sky." Anyone living further than 6 time zones away sees a completely different sky - unless you can see circumpolar stars that dip under the North Star. That means that you can see countries past the North Pole and down the other side of the globe.

Your zenith is yours - it is unique and changing all the time. Not even someone standing right beside you shares your zenith. You can use this idea of the zenith stars to comprehend the vast and mysterious experience of life on a sphere.

References

A list of extreme geographic points in the USA - Wikipedia - https://en.wikipedia.org/wiki/List_of_extreme_points_of_the_United_States

Comments

dc - April 2, 2021 at 10:32 PM

A lovely description of this idea of the mapping of latitude and longitude to celestial coordinates. “ Imagine the lines of latitude and longitude ballooning outward from the Earth and printing themselves on the inside of the sky sphere, as shown at right. They are now called, respectively, declination and right ascension.” from https://skyandtelescope.org/astronomy-resources/what-are-celestial-coordinates/

Sporades - Stars Not Part of Any Constellation

Sat, 24 Aug 2019 09:00:42 GMT

Milky Way behind trees. Photo by Ryan Hutton on Unsplash

Sporades definition

Webster's 1913 Edition has this funny little entry that defines sporades:

||Spor"a*des, noun plural. [L., fr. Gr. spora`des. Cf. Sporadic.] (Astron.) Stars not included in any constellation; -- called also informed, or unformed, stars.

Sporades - an obsolete word

This word no longer means anything.

This word has been removed from all dictionaries.

The International Astronomical Union (IAU) agreed in 1930 to include every known star within the boundaries of a constellation.

Sporades - the wild between constellations

Before that year there were wild places in between constellations where stars could exist. After 1930 all of the stars had been pinned down - like rows of dead butterflies. Every star is now "inside" a constellation boundary.

We don't need this word sporades any more; all the stars have been captured.

Comments

starinastar - August 24, 2019 at 4:27 PM

Guy Ottewell mentioned Allen's Star Names book. So ,I looked it up and found this web version. There is a chapter that talks about the evolution of the constellation names and it mentions the sporades: http://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Constellations*.html

Pingback: […] Zodiac Constellations zoomed in on Ophiuchus – the “13th” Zodiac Constellation between Sagittarius and Scorpio. The constellation borders (marked red) show how astronomers divide up the sky into named regions. […]

Zodiac Wavy Charts User Guide

Tue, 19 Feb 2019 09:00:26 GMT

I want to share this amazing object with you.

It's a skeleton key to the sky. It's a poster. It's a tome.

Guy Ottewell's Zodiac Wavy Chart 2019 poster

Guy Ottewell's Zodiac Wavy chart poster.

This poster is HUGE. 24 inches wide x 36 inches tall. Also, it's glossy and beautiful and full of engrossing details. You will return to this poster month after month and dwell on the intricate and scientifically-accurate renderings.

It is like a Moon Calendar but it shows the actual Moon position as well as its phase and date - plus it includes everything else in the sky. Best of all, it adds the “backdrop” of the zodiac constellations so you can see how everything moves among the stars.

The Zodiac Wavy Charts poster portrays the wildness of the Moon and its dynamic motion through the sky - all in a beautiful, informative, and rewarding wall hanging.

BUY the Zodiac Wavy Charts poster here - it's on sale!

Guy Ottewell's Zodiac Wavy Charts is a snapshot of the calendar month. Every day's events are “layered” onto a wavy band. Think of those wavy charts in 3-dimensions: You can pluck one off the page, stitch it together into a ring, enlarge it, and step inside it and you've got a view of the most interesting and active sky chart you've ever seen!

It's Better than a Moon Calendar

Moon Calendar 2019

In a standard Moon Calendar the day squares contain the Moon phase images. The Moon images can be arranged artfully, but mostly they are placed to make the Moon conform to the month; the Moon gets "captured" into our cultural calendar. You can see the phase and the day the Moon phase will happen. This is good as far as it goes... but the Zodiac Wavy Charts poster is 100x better!

Guy Ottewell's Zodiac Wavy Charts can tell you the day the Moon phase will happen. Also, it shows exactly where in the sky, and in which part of the Moon's orbit it will happen. It tells you which part of the Moon is titled toward you, if it's in an ascending or descending part of its orbit, and what constellation it is in.

This yearly calendar packs information that will teach you how to observe and will help you make sense of the sky. It's like having an expert astronomer on-call all year long.

If you don't have a Zodiac Wavy charts poster yet - you can order it here at Universal Workshop. The rest of this article will help people use the deep details on the poster to understand the motions of sky objects.

Quickstart Guide - Using the ZOD poster

Note: the Zodiac Wavy charts poster shows a northern hemisphere viewpoint. All writing here assumes you are in a northern hemisphere location.

Before you read this guide, please read Guy Ottewell's text at the bottom of the poster. It explains many of the key items visible in the chart and serves as a legend. Guy's writing provides a wonderful tour of the deep information revealed by these charts.

Unique Design Elements Tell the Story

The Sun's movement in 1 month.

Guy uses clever graphic design techniques to communicate how things move in the sky. For instance, to indicate how far the Sun moves in a month he expands the Sun with concentric rings. This clearly shows the sky location on the 1st of the month (the right edge of the outer yellow ring), the 16th of the month (the central Sun image), and the last day of the month (the left edge of the yellow ring).

The Moon's movement by day and libration.

Another unique design element (a variable-size red triangle) indicates the Moon's current libration - tilt - towards or away from the Earth. Knowledge of the Moon's libration helps observers see hidden Moon formations.

The Moon moves dynamically and this poster helps you really see that motion each day.

Spectral types shown on the poster.

Read the Charts from Right to Left

The Zodiac Wavy Chart should be read from right-to-left.

The Sun, Moon, and planets move (in general) from right to left across the sky. So too the Zodiac Wavy chart should be read from right to left. You can see the Moon phase images (and day numbers) grow from right-to-left. You can observe that the Sun moves from right-to-left over the month.

Sometimes when the Moon "overlaps" itself during a calendar month, the numbering looks a little funny - this happens because the calendar month is not the same as the Moon phase month (except February) the calendar month is always longer. This article about Blue Moons shows what happens when we try to squeeze the Moon into our monthly boxes.

The first and last wavy charts have lots of text indicating the constellation names, but the middle charts leave them out for clarity. If you want to find out which constellation a celestial object is "in" you can refer to the January or December charts.

Start with the Sun as the Anchor

Use the Sun as the anchor for understanding how to read the charts. Look to the left of the Sun image in each month. The space spanning 6 constellations to the left (east) of the Sun shows you the night sky at sunset. The space spanning 6 constellations to the right of the Sun shows you the pre-sunrise sky. The midnight sky is always centered about 6 constellations to the left of the Sun. You can imagine the whole of the night sky by centering your eye on the anti-Sun which shows the location of midnight on the 16th of the month.

The Sky at Midnight - Anti-Sun and the Full Moon

The anti-Sun indicates the meridian (the middle of the sky) at midnight. The anti-Sun also moves from right-to-left through the sky. It could be displayed with the same-sized concentric Sun rings. It marks midnight and you can see that the Full Moon is always close by.

Tilt the Poster to Line Up with the Sun

Here's a fun idea: turn the poster sideways and place it on an east or west wall at sunset to “see” the star band lined up with the rising “anti-sun” (east wall) or the setting "sun" (west wall). Anchoring to the Sun or the Anti-Sun may help you visualize how the Zodiac Wavy Charts poster shows you the whole sky of Zodiac constellations all at the same time.

Why is it Wavy?

Why is the wavy chart wavy? It's because of the way the ecliptic is tilted from the equator.

The meaning of the waves. It’s easier to imagine this if you think of the Equator as the horizontal and the plane of the solar system as tilted.

Eclipses - Every Six Months in the Same Sky

The location of eclipses = the location of node crossings = the location of the nodes = changes very, very slowly (18 years, 11 days, 8 hours to be exact).

Look at the eclipses - there are a few of them every year and 2019 is no exception! Notice that they all occur during the New Moon or the Full Moon and that they all occur in the constellations Gemini or Sagittarius. The reason the eclipses happen while the Moon or the Sun are in Gemini or Sagittarius is because of the Moon's orbital nodes. These nodes are "in" these two constellations this year.

It's not just the Moon that orbits the Earth, the Moon's orbit nodes themselves actually orbit the Earth. This orbit of the nodes takes 18.6 years! The intersection with the lunar phase cycle and the orbit of the Moon's apsides is the source of the famous Saros interval - where 2 similar eclipses occur.

So, if you buy the Zodiac Wavy Chart poster for the next 18 years, you'll see the Moon's orbital nodes - the location of eclipses - move through each of the fixed constellations!

Retrograde Motion - See it!

Planet motion is cool. Planets close to the Sun never cross the anti-sun, but outer planets do. This confused our ancient ancestors who did not realize that the planets were following an orbital path around the Sun at the same time that the Earth was following its own orbital path.

These two motions (the planet's and the Earth's) made it look like the planets sometimes moved backwards (retrograde)! You can find all of the retrograde motions easily and see exactly when and where they will happen.

Measurement - by Counting Constellations

Degree marking - the charts lack any of the standard degree measurements (Right Ascension/Declination or Altitude/Azimuth). This type of measurement is not really necessary for general use of these charts. This is because you can find these measurements in other places.

However, you may want to understand how big each section of the sky is compared to each section of the chart. You can think about it like this: there are 12 zodiac constellations (13 if you count Ophiuchus) and they span 360 degrees of the sky. We can see a bit less than 180 degrees of the sky at any one time so that's about 6 visible constellations! Just count about 6 constellations and you'll get about half the sky!

If you divide 360 degrees by 12, you get 30 degrees. So, an average constellation covers about 30 degrees of sky. And the sky moves at a rate of about 15 degrees per hour. That means it will take about 12 hours for the sky to completely change.

Want to figure out how big something is? Use your outstretched hand as a measuring tool. The distance from your thumb to your pinky (when your hand is fully-stretched out) is about 25 degrees - a little less than the average constellation width.

Analemma-ish

A subtle analemma appears.

One interesting after-effect of rendering the Sun's position in this "wavy" way is that you can see an aspect of the analemma. The slight movement in the Sun’s position month over month traces a very slim half-analemma shape across the poster. There is a very slight speed up and slow down that you can see if you look closely.

Here is an image of the poster showing the slight but noticeable curve that the Sun makes.

Sidereal Map - the Stars Stand Still

These Zodiac Wavy Charts create a sidereal map of the sky. Sidereal refers to the fact that the background of stars remains fixed through every chart while all the other objects move through them.

What do you see?

There are hidden treasures all through this gorgeous image. Share them with us when you find them!

Frequently Asked Questions

Why is the Zodiac Wavy Chart wavy? The charts are wavy because Guy wanted to show what was happening at the ecliptic. The ecliptic is tilted at 23.4˚ from Earth's pole (90˚ from the equator). So, sometimes objects in the ecliptic are below the equator and sometimes they are above it.
What is the Zodiac? The zodiac is the collection of constellations that define the ecliptic. The zodiac constellations define a band of sky where the Sun, Moon, and planets can always be found. Fun fact: Zodiac comes from the same root word that Zoo does - and it's called that because many of the constellations are animals.
Is this an astrology tool? No, this is a visual astronomy tool. Astrologers will certainly find this a useful poster to refer to, but it is designed for visual astronomy observation assistance.
What can I use this for? This astronomy poster is useful for many things! Mostly, it's a beautiful wall hanging that will draw your eye and reveal the deep celestial mechanics behind our Earth's motion through the solar system each year. It's also a wonderful conversation piece. Try telling people "It's like a Moon Calendar, but it works for everything else in the sky too!"
Can I order this Zodiac poster internationally? Yes - you may have to pay a little extra shipping and sometimes customs duties, but the poster can be shipped almost anywhere.
Does the site accept purchase orders? No, Universal Workshop does not accept purchase orders. You can pay by credit, debit, or paypal.
Can I order a 2020 poster now? Yes! Please contact Guy [at] Universal Workshop [daht] com or visit UniversalWorkshop.com and make a comment on one of the recent blog posts.
Can I order in bulk? Yes! Contact Guy Ottewell for details.

References

NASA Saros page - https://eclipse.gsfc.nasa.gov/SEsaros/SEperiodicity.html

Precession of the apsides - https://en.wikipedia.org/wiki/Apsidal_precession

Comments

Pingback: […] familiar with the ecliptic and the celestial sphere. The Zodiac is not just for astrology – astronomers use the constellations of the Zodiac to name 13 regions of the […]

Your Eyeball Sun - Scale Model of the Solar System

Fri, 21 Dec 2018 10:38:25 GMT

The Sun is the Size of your Eyeball

What would the rest of the solar system look like if you shrank the Sun to the size of an eyeball?

You are the center of the universe.

Well, at least you are for this scale model. You will be the Sun.

Imagine that the Sun shrank to the size of one of your eyeballs (about 24mm diameter) and it got placed inside your head. You are now the Sun, center of the solar system, looking out into the vast expanse of the solar system and space beyond.

Mercury is just 1 meter away - it is microscopic, essentially invisible at one tenth of a millimeter (0.1mm), the tiniest grain of sand. But if you reach out your arm and point your fingertip as far as it will go, you can almost touch it. Swing your arm around and you trace its orbit around your eyeball sun.

Venus is 1.86m (6ft) away - about the height of a tall-ish man. The second planet from your eyeball Sun is a little bit bigger than Mercury, but still almost invisible at the size of a single grain of fine sand (0.2mm).

Earth is 2.5m (8ft, 2in) away - just a bit farther away than Venus. You can't reach it with your outstretched hand; you would have to take a step towards it. Earth is also a little bit bigger than Venus, but not by much. And at this scale, the Earth is just another fine grain of sand so it's almost impossible to find anyway.

The Moon, smaller than Mercury, orbits just 0.6cm from the Earth sand. Imagine... your eyeball and two tiny grains of sand held in a 5m (16ft) diameter orbit.

Imagine all the empty space in the solar system. Imagine all humans on the surface of that Earth grain - and we have only visited the first 3 planets.

Mars is smaller than Earth and orbits 3.9m (12ft 10in) away. It is another grain of sand - with a red tint.

Jupiter is 13.4m (44ft) away. Imagine the outside length of a large school bus - that's how far away Jupiter is. Jupiter is the first planet in this scale model that is visible - it is 2.5mm diameter - at this scale, Jupiter is about the size of a small peppercorn.

Saturn is 24.6m (about 81ft) distant. It has shrunk to the size of half a sprinkle. This sprinkle crumb is far enough away from your eyeball Sun that you probably couldn't see it.

Uranus disappears at 0.8mm and 50m (162ft) away. It's about the size of a small ant's head.

Finally, we reach the similar-sized ant-head Neptune at 0.8mm which is an astonishing 77m (255ft) away at this scale. This is a bit closer than the entire length of a football field or a soccer pitch - Neptune would be at the other team's 20 yard line or 18 yard line respectively.

Summary

Close your eyes. Imagine your eyeball is the Sun.

All these tiny objects are orbiting your head at different distances in a more-or-less flat plane.

Out. In. Space.

References

Thanks to Guy Ottewell for his insights into how to use everyday objects to communicate the scale of the solar system - especially his groundbreaking Earth as A Peppercorn.

The Moon Hat Customer Images

Sat, 15 Dec 2018 14:23:01 GMT

Moon Hat photos sent in by customers and taken at Moon Hat events.

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Comments

Mike

This hat is awesome! Super soft! Stylish and educational!!

Mark Bright

Very attractive and yet educational hat. Helps visualize how what appears as a "Half Moon" is actually called 1st Quarter or 3rd Quarter Moon. Well made with style!

Cathy Deutchman

I love the moon hat! It's super comfortable, and fits inside my jacket pocket. When I wear my moon hat, I'm more likely to tune into the cycles of the moon.

Kristy Cohen

I teach a New Moon Meditation class and love to follow the orbit of the Moon through time. The Moon Hat will help keep me aligned with the phase and current constellations the Moon is located in--very cool!

Patricia

This hat is soooo soft and luxurious! Phases of the moon (tape instructions inside hat) are clearly illustrated. Easy ordering.

Rob

This hat is really nice -- it keeps my head toasty warm when running. Wicking is similar to the black diamond hat I used previously. Definitely recommend!

Stephen Marcinek

My kids love their moon hats! It is so wonderful that they are having fun in style and learning.

10 ways to wear a Moon Hat

Fri, 14 Dec 2018 12:00:03 GMT

Wear the Moon Hat - have fun!

The Moon Hat is no ordinary hat.

The Moon Hat keeps your head warm - yes! And, every day it gently reminds you to be curious about the Moon. It reminds you to observe what usually stays hidden. It reminds you to #doscienceeveryday.

There are many ways to wear a Moon Hat. You can wear the Moon Hat in at least 10 different ways. The Moon Hat is made of soft stretchy fleece with small embroidered Moon phase images placed all around the brim.

The Moon Hat fabric is flexible and foldable.

<div class="hat-gallery"> <figure> <img src="/images/blog/aHR0cHM6-moon-hat-style-moon-finder-473x1024.png" alt="The Moon Hat style The Moon Finder" /> <figcaption>Moon Finder</figcaption> </figure> <figure> <img src="/images/blog/aHR0cHM6-moon-hat-style-phase-reminder-473x1024.png" alt="The Moon Hat style The Phase Reminder" /> <figcaption>Phase Reminder</figcaption> </figure> <figure> <img src="/images/blog/aHR0cHM6-moon-hat-style-hidden-moon-outside-473x1024.png" alt="Moon Hat hiding all embroidered Moon Phase images" /> <figcaption>Hidden Moon (outside)</figcaption> </figure> <figure> <img src="/images/blog/aHR0cHM6-moon-hat-style-hidden-moon-inside-473x1024.png" alt="Moon Hat with brim folded inside hiding phase images" /> <figcaption>Hidden Moon (inside)</figcaption> </figure> <figure> <img src="/images/blog/aHR0cHM6-moon-hat-style-tidal-shores-no-tag-473x1024.png" alt="Moon Hat longshoreman style inside-out with brim folded up" /> <figcaption>Tidal Shores</figcaption> </figure> <figure> <img src="/images/blog/aHR0cHM6-moon-hat-style-tidal-shores-show-tag-473x1024.png" alt="Moon Hat longshoreman style with instruction tag visible" /> <figcaption>Tidal Shores (tag)</figcaption> </figure> <figure> <img src="/images/blog/aHR0cHM6-moon-hat-style-moon-slouch-473x1024.png" alt="Moon Hat pulled backward for relaxed slouch style" /> <figcaption>Moon Slouch</figcaption> </figure> <figure> <img src="/images/blog/aHR0cHM6-moon-hat-style-moon-beret-473x1024.png" alt="Moon Hat pulled forward for beret style" /> <figcaption>Moon Beret</figcaption> </figure> <figure> <img src="/images/blog/aHR0cHM6-moon-hat-style-moon-disk-473x1024.png" alt="Single Moon Phase image showing at back of head" /> <figcaption>Moon Disk</figcaption> </figure> <figure> <img src="/images/blog/aHR0cHM6-moon-hat-style-moon-peeker-473x1024.png" alt="Moon phase disk peeking out from ear area" /> <figcaption>Moon Peeker</figcaption> </figure> <figure> <img src="/images/blog/aHR0cHM6-moon-hat-style-halfsies-473x1024.png" alt="Half the Moon Hat brim folded to hide four phase images" /> <figcaption>Halfsies</figcaption> </figure> </div>

10 ways to wear the Moon Hat

Moon Finder - where is the Moon right now
Phase Reminder - what is the Moon phase right now
Hidden Moon outside - hide the moons outside
Hidden Moon inside - hide the moons inside
Tidal Shores no tag - longshoreman style
Tidal Shores show tag - longshoreman style
Moon Slouch - Moon Finder, pull the fleece backward
Moon Beret - Moon Finder, pull the fleece forward
Moon Disk - Hidden Moon inside, show one embroidered disk
Moon Peeker - Hidden Moon inside, peek one embroidered disk
Halfsies (Bonus #11) - Hide half the phases, wear the hat straight

#1 - The Moon Finder

The standard way to wear the Moon Hat with the new Moon image in front. This creates the model of the Moon, Earth, Sun relationship and helps you understand how the motions of the Moon create the phases that we see from Earth.

Get the current Moon phase. Put the hat on with the New Moon image on your forehead. Face the Sun. Now, all of the Moon phase images point to where the Moon is in the sky. Amazing!

#2 - The Phase Reminder

This everyday style is for people who want to remind themselves of the phases of the Moon and how they change over the 29 and a half days of the cycle. Just choose a Moon phase and put it at the front.

This is a subtle way to keep track of the Moon phases and learn their sky location. Before you put on the hat, pause for a second and consider which phase to wear. And, it doesn't feel like a Moon phase quiz - it's fun to put your thinking cap on!

#3 - Hidden Moon outside

Don't want any Moon phases to show? Just fold up the brim toward the outside of the hat and all of the Moon phase images disappear.

Sometimes a hat is just a hat.

#4 - Hidden Moon inside

Another way to hide the Moon phase images... tuck the brim of the Moon Hat towards the inside. All the Moon phase embroidery is now hidden and you have a sleek cap.

Looking for a unique style? The Moon Hat is flexible.

#5 - Tidal Shores no tag

This is the longshoreman style. Turn the Moon Hat inside out and then fold the brim outward. The brim should be wide enough to both show the Moon phase images and hide the instruction tag.

A close-fitting style that uncovers your ears.

#6 - Tidal Shores show tag

Just like the Tidal Shores no tag, but the brim of the hat is folded thinly so that the tag is revealed. You can wear the tag on the side, or the back, or if you are feeling daring, on the front!

This style makes a strong statement - show off the instruction tag.

#7 - Moon Slouch

This is the Moon Finder style, but pull the Moon Hat upwards to get some amount of fabric standing up away from your head and then pull it backward and flatten it for a sleek look

You can easily wear the Moon Hat pulled up above your ears.

#8 - Moon Beret

This is the Moon Finder style, but pull the Moon Hat upwards to get some amount of fabric standing up away from your head and then pull it forward and flatten it for an intense look.

Folding and bunching the fabric in the hat leads to a renaissance or jester look.

#9 - Moon Disk

The Moon Disk style starts with the Hidden Moon inside, but then you pull the embroidered disk of your favorite Moon phase and place it somewhere - it could be centered on your forehead or placed round the side of your head just behind the ear, or all the way at the back. It's your choice.

This style lets you show an individual Moon image disk.

#10 - Moon Peeker

This style is the same as the Moon Disk, but pull the Moon phase under the fabric of the brim until it is just peeking out. This style looks particularly good when the disk is just in front of your left or right ear.

This look makes a sly statement.

#11 - Halfsies

Fold down half the Moon Hat brim to hide 4 of the phases, then adjust, and angle the hat so that it looks like it is sitting flat on your head.

An alternative way of hanging your hat.

Go out and play with the Moon Hat

This is a fun and flexible bit of fabric with lots of science and a mountain of style potential. Hide and show the Moon phase images, fold and flex the fabric. Get outside and get curious about the Moon and its motion.

Feel the Earth spin

Tue, 09 Oct 2018 12:15:20 GMT

Many people ask "Why can't I feel the Earth spinning?" Or "Why don't we feel the rotation of the Earth?" The answer is that the Earth is so large and we are so small in comparison that we just get carried along for the ride.

We humans are tiny so we don't notice that everything on Earth moves along with us. Until we look up and we see the Sun speeding through the sky - then the questions start to fly: "Why does the Sun move across the sky?", "How big is the Earth?", "How fast is the Earth spinning?"

Q: If the Earth is spinning why can't we feel it? A: The Earth is gigantic and we are tiny.

It's hard to imagine just how large the Earth is and just how fast it is carrying us around in its daily motion. How fast is the earth spinning?

You are about to learn the answer and learn how to experience this speed!

We are too small to see the illusion

The Earth spins at about 1000 mph (1609 kph) at the equator. But we can't feel it. This illusion of non-motion happens for several reasons:

Because the Earth is enormous compared to us, and
Everything around us moves in the same direction and speed, and
Our inner ear is not sensitive enough to feel the gradual changes in momentum caused by Earth's constant turning.

Imagine riding in a fast car that has no windows. The car cruises on a smooth highway at 100 kph (62 mph). Inside the car we chat with our friends, the seats are comfortable, and maybe a hot drink sits placid in a cup holder. We don't feel the motion at all unless the car turns or speeds up or slows down.

Everything seems to be staying still but this stillness is an illusion. All of this stuff in the car is moving along with us at the same speed. But, if you could open a window in the car you would see the motion of the other objects not in the car.

The sky is our open window to find those other objects that are not "on the Earth." We will use them to explore the Earth's speed and movement.

Motion senses don't feel the motion

Another reason that we can't feel the Earth spinning is because our sense of balance. We get this sense from organs of the inner ear. We know what it feels like to move. We can feel a car accelerate and turn - but these sense organs don't help us feel the Earth's changes in speed and constant turning.

It's easy to feel and then believe that the Earth stays still and everything else moves around us; the Earth doesn't seem to be moving. The idea of a moving Earth seems preposterous. It's no wonder it took humans so long to figure out that the Earth is spinning and moving!

However, you can learn a surprising way to feel the rotation of the Earth - and it has to do with the speed of sound. You can "feel the Earth spin under your feet" and all it takes is a little bit of imagination.

Speed of sound is the speed of day

The speed of sound in air is 1235 kph (767 mph). This is really fast, but it is still a visible and imaginable speed.

The speed of the Earth's rotation at the equator is faster than the speed of sound! But, because of the Earth's shape, the Earth's rotation speed is exactly equal to the speed of sound at two latitudes on the Earth: 42.97 North and 42.97 South.

What does this mean for you and your approach to physical astronomy? You have to train your brain to see the speed of sound, then you will be able to feel the Earth spinning. You will understand that the speed of sound is the speed of day.

7 ways to see the speed of sound

We can train our brains to "see" the speed of the Earth's rotation (I've named this speed the "Speed of Day"). This is possible because "the speed of sound = the speed of Earth spinning."

You see lightning before you hear thunder because of the speed of sound. Credit: FreePhotos

The fastest plane you've ever seen is traveling a bit slower than the speed of sound. Imagine the fastest jet plane you have ever seen. Unless you were watching a fighter jet, that jet was not going at the speed of sound. Commercial jet planes travel about 250-350 mph below the speed of sound.
Echoes, echoes, echoes... The speed of sound can be heard and easily visualized by exploring sound echoes that bounce off walls, fences, hillsides, and other objects.
Large fields. Go to a large field (as big as a football field or bigger) with a friend and ask them to clap. You will see your friend's hands clapping and then hear the clap.
Stadium concerts. You can experience the speed of sound at big stadium concerts where you can see the drummer hit the drums but the sound is not in synch with what you see.
Lightning and Thunder. You can feel the speed of sound when you see the flash of distant lightning and you don't hear the boom of thunder for several seconds. Every 5 seconds is about 1 mile.
Fireworks. You can witness the speed of sound when you are watching fireworks and you hear the bang of the explosion after you see the light of the explosion.
Videos. Finally, there are several good videos online that can help you visualize the speed of sound (links below - includes a clever piece from the Exploratorium in San Francisco).

The speed of rotation of the Earth

How fast is the Earth spinning? Once you have a clear idea of how fast sound goes, you can get a clear idea of how fast the Earth is spinning - and by experiencing this speed you can easily imagine just how incredibly large the Earth is.

A gigantic bell rings, "Races the day"

Bell, Sun, Mountain - the speed of sound is the speed of day. Credit: vasocardin

One way of visualizing the speed of the Earth's rotation is to imagine that a gigantic bell rings each time the Sun enters a new time zone. Imagine that there is no sound loss over distance and the sound of that bell can be heard across the whole time zone (up to 1000 miles).

When this bell rings, the sound takes time to travel. It will travel at the speed of sound: 767 miles per hour.

Sound = 767 miles / hour

Bangor, ME and Detroit, MI - two American cities on opposite ends of the eastern US timezone - are 1183 km (735 miles) apart. The sound of our imaginary bell takes about 1 hour to travel between these cities.

Earth surface = 767 miles / hour

Since these cities are near 42.97 N latitude, the Earth takes about 1 hour to spin underneath the Sun.

Why can't we feel the Earth spinning when it is moving faster than the speed of sound?

Sound, which seems quite fast, is actually slow enough to "see" it moving. Once you can see the speed of sound you have seen the speed of the surface of the Earth.

Summary

The Earth rotates once per day. People at the equator are moving at faster than the speed of sound, people near the poles are moving slower than the speed of sound. People living at latitude 42.97 N and 42.97 S are moving at exactly the speed of sound.

References

Editor's Note: Credit goes to Bob Berman (aka SkyManBob) for first pointing out the latitude/speed of sound correspondence to me. I first learned about this idea in his fantastically engaging book Zoom - How Everything Moves. It has a footnote in Chapter 5 that says people at Coney Island are moving at 795 mph - just over the speed of sound. It got me wondering... how can people experience this speed? The result is this article. Thanks, Bob!

Editor's Note: Another Bob (aka AstroBob) gets credit for helping me refine this article with insights about our common perception of motion.

List of cities at 43˚N latitude.

Calculations showing speed of rotation at different latitudes on the surface of the Earth.

Video showing how to use your video camera to measure the speed of sound - good science fair project!

Video by the Exploratorium visualizing the speed of sound in a very creative way - Clapping Speed of Sound.

A visualization of the Earth's surface rotation speed at each latitude.

A general audience article discussing how we experience the motion of the Earth.

Comments

Jim - October 10, 2018 at 10:28 PM

Another way to visualize the speed of the turning earth: For convenient math, let's say you live where the earth turns 720mph (nudge the results up or down as appropriate for your location). 720mph is 12 miles/minute, or 1 mile every 5 seconds. Now choose a spot you know well in your local landscape that is directly east of you by anywhere from a mile to several miles. You can now imagine your location rolling directly toward that spot at 5 seconds per mile (say hey: the good old lightning rule of thumb speed of sound Daniel was talking about!); my spot (a point on the shoreline of the Atlantic) is between 20 and 25 seconds of Earth rotation time away.... You know, 5 seconds to go a mile is not all that fast—your imagination can definitely keep up!

starinastar - October 11, 2018 at 7:48 AM

Hi Jim! I like the way you describe the experience of looking at a spot about a mile away "rolling directly toward that spot at 5 seconds per mile." It's a reversal of what we normally experience which is: the Sun traversing the sky each day. I love to get people thinking about the movement of the day as a speed; the "speed of day."

bkellysky - December 6, 2018 at 10:19 AM

Wow! I wish I had seen this before our religion class talked about Joshua getting the Sun to stand still. We talked about why we don't feel the earth's rotation or our movement in the solar system. I also calculated we could make the sun stand still in the sky by going about 13 miles from the north pole and walking westward at about 4 miles an hour. If we could keep that up for 24 hours (and do this when the sun is up over the polar regions), the sun would appear to be in the same spot in the sky all day as we walked. The earth would literally be rotating under our feet, making this the ultimate treadmill trek.

starinastar - December 6, 2018 at 10:45 AM

Hi Bob! I love that image of walking around the North Pole - that's a 41 mile trek. I could imagine a ship enacting this in the summer time! That would be a fun event to try to organize. Dan

How can I see Venus?

Mon, 01 Oct 2018 12:05:58 GMT

You can see Venus in the sky at two times and locations:

in the early evening, shortly after sunset in the west or
the early morning, shortly before sunrise in the east.

Venus orbits the Sun and moves from evening sky to morning sky and back again over the course of about 18 months. Venus makes beautiful sweeping motions in the sky that reveal secrets of the solar system.

See Venus, see the plane of the solar system

The planets all orbit the sun in the same plane. Image not to scale.

All the planets in the solar system orbit the sun. All of the orbits line up in neatly nested concentric rings. And all of the rings are lined up with each other as if they are placed on a single surface together.

The orbits are all in the same plane. It's like they are all marbles circling around the sun on the same giant plate. This is called the "ecliptic" and it is visible in the sky if you know how to find Venus.

Intersecting space planes

The "space plane" is not an airplane

The "plane" is a tool you can use to see the way things move in space. This "plane" is not an airplane, but a flat slice of space.

Here is an image of two intersecting planes. Imagine the blue plane is the earth's surface and the brown plane is up-and-down from ground to sky.

Each object (and movement) in space creates a "plane," an imaginary slice through physical space. The blue "plane" above looks like the surface of a pond, lake or ocean. A wall or roof of a house is a plane. A dinner plate is a plane. Stretch your arms out and spin in a circle and you have created a plane with your arms.

There are planes in space everywhere.

Your own personal space plane

You create a plane with your vision and balance. You can imagine a flat surface like the surface of a pool of water and your eyes are just above the waterline. This surface moves and tilts when you move your head.

Your head has two eyes that define your plane of vision. Also, your body is oriented to gravity because of your sense of balance - the "personal horizon" is the first plane for you to orient to. Your body naturally coordinates your visual sense with your sense of balance and gives us the sense of being located level on a surface. This is the "sense of horizon."

A new horizon - choose a plane!

To get good at Physical Astronomy, we have to learn to coordinate our main "personal horizon" plane with other planes of the earth, moon, solar system, galaxy, and universe.

The earth for instance, has a lot of planes, the range of latitudes, the north and south poles, the Arctic and Antarctic circles, the equator, the tropics, a range of longitudes, the prime meridian, the international date line, the ecliptic, the galactic plane and more.

To keep things simple, let's focus on just one other plane for now: the plane of the solar system. A wonderful thing will happen when you learn to link the plane of vision with the plane of the solar system. It's pretty easy to do, and it's a skill that gets better with practice.

The key to linking vision and solar system planes is to know that the plane of the solar system is visible as the ecliptic. One easy way to see the plane of the solar system is to see the bright inner planet Venus.

See Venus and you can see the orbit of Venus

See Venus and the Orbit of Venus

Venus is closer to the Sun so we are able to see its entire orbit. Actually, we can't quite see the entire orbit because sometimes it goes in front of the sun and sometimes it goes behind the sun.

We can see Venus in the early evening and in the early morning. Venus is visible in our sky when it is at the left and right extent of its orbit around the sun. We only see Venus in the sky when it is swooping around the left or right of the sun.

If you want to see the orbit of Venus and see the plane of the solar system you can do it! All you have to do is imagine a line connecting Venus to the Sun.

If you are looking at Venus early in the morning before sunrise or early in the evening before sunset, the process is the same. Imagine a line connecting Venus to the Sun; this is the ecliptic. Venus's entire orbit covers roughly 1/4 of the sky.

Summary

We learned about two main planes in space: your personal horizon (which changes as the Earth carries you around the Sun) and the plane of the solar system: the ecliptic.

By learning to visualize these two space planes, we can begin to experience the extremely large dimensions of space.

References

Venus information from In the Sky.

How many stars are in the sky? A Quiz

Mon, 24 Sep 2018 12:00:01 GMT

Have you ever looked up and wondered how many stars are in the sky?

How many stars are in the sky right now?

It's a simple question with a surprising answer!

This question has layers of answers - the most common answer is "it depends" - it depends on where you are, what part of the year it is, what time it is, and most of all... how dark are your skies and how powerful is your telescope?

Let's start with a quick (approximate) list of how many stars you might be able to see at once at night under "normal" conditions with no telescope. (The details on these calculations are near the end of this article.)

How many stars can I see at night:

The most stars anyone can see from the Earth (no telescope): 3700
The number of stars can you see at a dark sky site: 2000
How many stars can I see in my suburban yard: 200
How many stars can I see in a large city: 20

Another trick answer to "how many stars are in the sky?" is: "all of them!" All of them are in the sky, but they are just not visible to you "right now" for one reason or another.

I know, these answers are not quite what you may be looking for. Let's look a little bit deeper by starting our search for how many stars can I see at night.

Quiz - How many stars are in the sky, how well do you know them?

Let's start by taking a short quiz (answers are just a scroll away, so don't peek!):

Which star is the brightest in the sky?
Which star is the closest to us?
Which star is the first one discovered to have a planet supporting life?
Which stars have a solar system?

Scroll down a bit to see the answers to this first part of the quiz.

While we are waiting to scroll (and to keep the peekers from peeking!)... let's talk a little bit about how professional astronomers count the stars.

Annie Jump Cannon - Harvard star counter extraordinaire

Annie Jump Cannon - Harvard University Image: Public Domain

Have you ever tried to count the stars? If you have, you probably gave up at some point because there were too many to keep track of.

In the early 1900s there was a tenacious Harvard astronomer named Annie Jump Cannon who didn't give up counting! In fact, she counted so many stars that she almost lost track.

To keep everything organized she started categorizing them by their colors. She invented the spectral classification system - O,B,A,F,G,K,M - and personally classified over 350,000 stars!

Her method of categorizing stars is still in use today.

The answers to the star Quiz

The Sun compared to other stars. Image: Daniel Cummings

The number of stars in the sky is...

SPOILER ALERT! - Here are the answers to the quiz above!

The quiz is a trick quiz because the answers to are all "the Sun." If we don't include the Sun in this quiz then we get very different answers and the answers are:

Sirius is the brightest star (it is almost as bright as Jupiter),
Proxima Centauri is the closest star (it is 4.22 light years away),
No star's exoplanets have yet been proven to support life - the Sun is the only star so far to host life.
There is only one solar system. The answer to question 4 is truly a trick question: "No other stars have a solar system... because only one star is named "Sol" ... the Sun! The "Solar System" is named after Sol - the Sun. See: Sol+ar = Solar. Other stars would have planetary systems named after the star. For instance, there may be a "Sirius-ar system" that hosts a planet like Earth.

The Known Universe

Ok, now you are done with the quiz let's get counting stars. Go outside, look up, start counting!

Artist's conception of the known universe. Credit: Pablo Carlos Budassi via Wikipedia

Before, we start... There is one tiny problem with counting the number of stars. Even with the best tools humans have invented, we can only see a small part of the universe. Astronomers call this the "known universe" and it stretches about 14 billion years back through time in one direction, and (we assume) 14 billion years back in another direction.

Ten sextillion stars in the known universe

Astronomers have estimated the number of stars in the Milky Way galaxy as one hundred billion (this is a low estimate by the way). The Milky Way is an average galaxy. Astronomers estimate that there are one hundred billion galaxies in the known universe (another low estimate). The math to figure out the total number of stars in the universe is as simple as the result is mind-boggling!

100,000,000,000 (one hundred billion - 11 zeros) x 100,000,000,000 (one hundred billion - another 11 zeros) = 10,000,000,000,000,000,000,000 (ten sextillion - 22 zeros)

Counting to one million is not like Counting to one billion

A million is way, way smaller than a billion.

It would take 11 days to count to one million if you counted one number per second without doing anything else. Counting to a billion at the same pace (one per second) would take you 32 years of continuous counting!

Count to 1 million at a rate of 1 per second = 11 days
Count to 1 billion = 32 years

- Arithmetic

If you counted all the stars in the Milky Way at the rate of one per second, it would take you about 3200 years to finish counting our one galaxy's set of stars.

How many stars in my sky now?

Ok. So, let's get real. Now we know how many stars there may be in the entire known universe, let's narrow the question.

Here is how we will narrow the question. Let's create a set of ideal conditions that will guarantee we see as many stars as possible.

This is the set of almost ideal seeing conditions. This set of conditions would guarantee seeing the most number of stars that anyone could ever see with the naked eye:

I am on a tall mountain top with no trees looking up at the perfectly clear and calm sky right now. It is midnight. I can now see approximately half the stars in the sky. These near perfect seeing conditions make it so that I can see stars to magnitude 6 with my 20/20 vision.

Number of stars in the sky I see

According to David Haworth of Stargazing.net there are approximately 7400 magnitude 6 or brighter stars. Remember, we can only see half the sky at any time. So, cutting 7400 in half we get 3700 stars. 3700 stars is the greatest number of stars that any earth-bound human can ever see at any one moment without a telescope or other aides.

Stars in my sky right now

Now we know how many stars you might ever see at once, let's look at how most people see the sky.

Most people cannot see 3700 stars because of serious light pollution, horizons full of trees and landforms, and atmosphere, lots of watery, moving atmosphere floating above us.

If you are lucky and go camping in a dark sky area you might be able to see about 2000 stars on a good night.

In a typical, light-polluted suburban sky you can see approximately 200-300 stars.

In the middle of a big city the number of stars goes down to about 12 to 20.

12 Stars.

12. That's not a lot of stars. Maybe take a trip out of the city to see the stars?

Summary

You can see 3700 stars under perfect viewing conditions.

You can see about 2000 under excellent dark skies.

You can see about 300 stars in the suburbs.

You can see 12 stars under bright city lights.

References for how many stars

Stargazing.net - David Haworth compiled data on the number of stars at each magnitude and presented it in a nice table.

Sky and Telescope article - covers skyglow, light measuring technology, light maps, NELM and more. Authoritative.

Space.com article - how astronomers estimate the number of stars in the Milky Way.

National Geographic Kids - Mini article on light pollution with estimates on how many stars are visible from different places.

Comments

starinastar - October 1, 2018 at 9:04 AM

I just found this page that gives you detailed instructions about how to use a cardboard paper towel tube to get an accurate count of stars in your sky in about 5 minutes: http://www.projectdarkskies.org/pipe.htm

Track the Sun

Mon, 20 Aug 2018 12:20:12 GMT

So you want to track the Sun?

Sunrise at Stonehenge. Image credit: Pixabay.com

You don't need to build your own Stonehenge. You can track the Sun's position in the sky and learn how to do astronomy during the day!

Let's get started with the basics of sun tracking. Here is everything you need to know to begin:

The Sun does not move; the Earth moves - it carries us under the Sun - it just looks like the Sun is moving.
The Earth moves every second of every day so the position of the Sun changes every second of every day.
Night is not the "Sun going away", it is the Earth blocking the Sun.

One Day of Observation: the Sun rises and the Sun sets

Let's start with a few easy observations about daytime. These are things you can notice just by waking up early one day before the Sun brightens the night.

The Sun starts the day for us on one side of the sky and ends the day on another side. At both of these times (sunrise and sunset), the Sun appears near to the ground - at the horizon.

During the middle of the day, the Sun appears to move "up" and across the sky and then back "down" again. In the middle of the day - at noon time - the Sun is high up in the sky, away from the ground.

Shadows change during the day

In the morning the Sun makes long shadows. At noon the Sun makes short shadows. At the end of the day, the Sun makes long shadows again.

With a few simple tools you can measure the Sun's position and shadows.

The Sun moves east to west

Over the course of one day, the Sun appears to move across the sky from east to west, rising to the highest point at noon. The Sun's light shines on the Earth and makes shadows that move and change position and size. As the Sun "moves" through the sky, the shadows move on the ground.

Build a simple sundial, track the Sun

Sundial - Krk, Croatia. The gnomon (stick) casts shadow on marker at XII 12 o'clock noon. Image credit: Pixabay.com

A sundial tracks the shadow of the Sun with an object that casts a shadow and time markings. For the simple sundial you can use a stick. The shadow of the stick (the stick on a sundial is called a gnomon) moves across the sundial. The shadow of the stick points to the time markings.

The simplest sundial is just a stick stuck in the ground with time markers nearby. The location of the stick's shadow moves across the time markers throughout the day.

A stick, the Sun, another stick marks shadow. As simple as it gets. Image: Jim Champion

Mark the shadow's position with any object (chalk drawing, a rock or another stick is a good choice). In the morning, the Sun appears low in the east and the shadow is long. The morning shadow points toward the west. At midday (noon) the Sun is at the highest point so the shadow falls in the middle and becomes short. At sunset, the shadow becomes long again - pointing to the east.

Paper Plate Sundial

Push a pencil through a paper plate to make a sundial. Image Credit: Daniel Cummings

A paper plate with a pencil stuck through the middle makes a great moveable sundial! (Remember, when you move a paper plate sundial, you have to be careful to place it in perfect north-south alignment.)

Take this outside on a sunny day, then make a mark on the paper plate at the top of each hour. The shadow will move slightly each hour. The mark should go at the middle of the pencil shadow.

When you have completed this during one sunny day, you have made a sundial that can tell the time - roughly speaking!

An indoor sundial - the Sun Tracker

Most people think of sundials as something that you place outside. But, the Sun shines inside through windows. You can track the Sun through a window.

An indoor sundial can help you track the Sun from the comfort of your own home! Do you have a sunny (or partly sunny) window? You can track the Sun and reveal the secrets of the Earth's motion.

The Sun Tracker is an easy-to-use indoor sundial. Place the glistening window cling on any sunny window and then mark the position of the window cling's shadow using one of the included stickers.

Repeat the next day or the next week at the same time of day. You will see a pattern emerging: the shadow cast by the Sun moves quite a bit each day.

If you are extra precise with recording the shadow at the same time of day, and you are able to do it for an entire year... you will see the Analemma.

The Sun Tracker is like a little bit of Stonehenge for your window.

Summary

Track the Sun with simple tools and you will reveal the motion of the Earth. There are two main motions of Earth, daily rotation and yearly orbit. Earth spins under the Sun each day and around the Sun in an orbit each year.

It is these two motions that make the Sun seem to move in the sky. Remember that the next time you are looking for the Sun - it's where it always is... the Earth is what moves.

8 Ways to Find the North Star

Fri, 27 Jul 2018 12:15:50 GMT

Find the North Star

You can use these 8 ways to find the North Star (Polaris). These are all fun ways to find the North Star. The North Star is special because of its position in the starry sky.

A long exposure photograph showing all of the other northern sky stars circling around the North Star. Image provided by ESO.

8 ways to find the North Star

Look north and guess - you can find the North Star in a relatively dark region of the sky and there are not many other bright stars around it. If you are south of the equator, head north before you try to look for the North Star because you won't be able to see it until you get the Earth out of the way.
Use the Big Dipper cup stars as pointers. This is the classic way to find the North Star. The two stars of the Big Dipper cup are known as the "pointer stars" and they show you which star is the North Star. The North Star is about 5 lengths of the pointer stars away.
Camera timelapse - ooh! I love timelapse. A great timelapse of the night sky is an unbeatable way to relax. By taking a timelapse of the starry sky you can detect the apparent motion of the stars. If your timelapse covers enough of the sky (with a wide angle view) chances are that you will be able to identify the North Star because it is the star that moves the least.
Phone app - grab a planetarium app like SkySafari. Almost every star app these days has a "Augmented Reality" view that you can use to find Polaris. Just use the AR method of holding the phoone up above your head and searching around or you can type the name of a star into the search box in the app.
Observe the sky, patiently measuring the movement of every star. The one that moves the least is Polaris. This might take a long time because the stars move pretty slowly.
Mark a known spot as your North Star viewing spot. This is easy to do with a product like the Star Spot. You can return to that spot any time of day or night to sight the star - the North Star is always in the same place in the sky.
The North Star is located in between the two easy-to-identify constellations The Big Dipper and Cassiopeia - the Queen.
Memorize its color and the stars around it - this is easier than it sounds! Polaris is a yellow supergiant and has a faint yellow tint. Also, the North Star is located in a region of the Milky Way that has fewer stars so it is surrounded by dark areas of the night sky.
A reader has suggested a 9th way! Create the Summer Diamond. Add a new triangle to the Summer Triangle asterism by using the North Star as a new point. Suggested to me in January 2023 by Peter Birren (Author of the wonderful Objects in the Heavens astronomy book) see below for an illustration. This method is most useful in the summer and early fall months because that is when the Summer Triangle is most visible.

Find the North Star using new asterism - the Summer Diamond. Proposed by Peter Birren.

The Standard way to find Polaris, aka the North Star

Here is the classic way to find the North Star! Use the pointer stars of the Big Dipper. This is a reliable method for finding the North Star that has been taught to generations.

Find the Big Dipper to find the North Star

Look at the two stars in the picture below. One is Dubhe - which is labeled a for alpha, and the other Merak - which is labeled b for beta. These form the outer lip of the Big Dipper's cup. These two stars can be used to create an imaginary line to "point" at the North Star.

The distance from the pointer stars to the North Star is about 5 times the distance between Dubhe and Merak.

The North Star is shown in this image as a red dot labeled "Polaris."

Use the two pointer stars of the Big Dipper to find the North Star (Polaris). Picture credit user Bonĉ source Wikipedia

These instructions work for the 80% of people who live in the northern hemisphere - anywhere north of the equator. For the 20% of people who live in the southern hemisphere the North Star is not visible because it is blocked by the Earth. As you move south toward the equator (and eventually move past the equator), the North Star gradually sinks lower in the sky until it stays completely below the northern horizon.

The North Star and the South Star

However, there is a kind of "south star" and if you live in the southern hemisphere you can use that star to find due south! There will be another article teaching how to find the "south star."

The North Star has been known by many names

The North Star is also known as Polaris, the Pole Star. Its official name is Alpha Ursae Minoris (named Alpha because it is the brightest star of the Little Bear), but - according to this list gathered by astronomer Chris Dolan - it has also been called these deliciously mellifluous names: Alruccabah; Cynosura; Phoenice; Lodestar; Tramontana; Angel Stern; Navigatoria; Star of Arcady; Yilduz; Mismar.

The North Star is unique because it stays almost perfectly still

Find the North Star in the night sky by finding the star that moves the least. All the other stars appear to move through the sky in great arcs during the night. The North Star barely moves during the night. This is because the Earth's axis points directly at the North Star.

That means that if you could visit the north pole and look directly up you would find the North Star right above your head! The North Star stays in the same place no matter where you see it from on Earth.

Star trails around the North Star as seen from near the North Pole. Credit: David Malin

The North Star is unique because it is in a dark part of the sky

Once you learn how to find the North Star you may find it easy to find again. This is because the North Star is in a dark part of the night sky and there are not very many other bright stars around it.

Myths about the North Star

"The North Star is the brightest star in the sky." - Nope, that distinction belongs to Sirius, the Dog Star. The North Star is the 50th brightest star. The North Star is still quite bright and it is easy to find.
"The North Star will always be the North Star" - This is a myth. In fact, there have been several "North Stars" throughout recorded history. The ancient Egyptians saw Thuban as their North Star.
"There is a South Star." - While there is a star located close to the southern pole position (two stars in the Southern Cross point to the faint star Polaris Australis in the constellation Octans), it is not nearly as obvious or famous as the North Star.

The North Star is a very special star! We learned how to find it.

Where is the Sun?

Wed, 27 Jun 2018 00:32:05 GMT

Where is the Sun right now?

Can't see the Sun? Maybe there is something blocking it. Here is a list of 10 surprising things that can block the Sun.

Things that block the Sun.

Where is the Sun during the day? On a clear day, this is a very simple question. The Sun is "up there" in the sky - it's a big, bright, fiery ball and it's generally a yellowish orange color. You just point to it - there it is, up in the sky, the Sun.

However, many things can block the Sun. Usually, it is clouds that block the Sun, but not always. Let's take a tour of the astonishing number of things that can block the Sun.

A list of things on Earth and in space that can block the Sun

During a cloudy day you can't always tell where the Sun is. The day goes by in a dull gray haze. In fact, some people who live in cloudy places like Seattle, Washington often wonder "Where is the Sun?" In fact, it's cloudy in Seattle 308 out of 365 days of the year.

Sometimes other things besides clouds can block the Sun. These are mostly things that fly or float in air or space. There are small, flying animals like birds, bugs, and bats that can get in between us and the Sun.

Human-made objects like drones, balloons, airplanes, helicopters, rockets, bombs, and blimps can stop the light of the Sun from reaching us for a moment.

Smoke from a large fire, steam from a power plant, or ash clouds from a volcano will blot out the Sun for longer periods.

An asteroid can fly between the Earth and the Sun.

Most famously, the Moon can block the Sun in a total solar eclipse.

Image of the Total Eclipse August, 21, 2017 as seen from Folly Beach, SC - Image Credit Wyatt Cummings

The two inner planets - Mercury and Venus - will sometimes cross the face of the Sun (astronomers call this a "transit"). They seem very small against the disk of the Sun. Here is a side-by-side comparison of the two most recent transits (photo composite by Ender Gökçebay).

A composite of Venus transit and Mercury transit showing relative sizes as seen from Earth. Credit: Ender Gökçebay.

Image credit Guiseppe Donatiello - public domain Wikipedia

Finally, we come to the largest Sun-blocker of all: the Earth. The Earth blocks the Sun every single day! In fact, it happens so often that long ago humans gave it a special name: when the Earth blocks the Sun, people call this "night."

The Earth blocks the Sun. It is night.

Where does the Sun go at night?

During the night, this question of "Where is the Sun?" gets a little bit more complicated. The Sun still exists - it doesn't "go out" like a candle or a fire. The Sun is hidden from our view at night by a very large planet - the Earth. We cannot see through the Earth so it blocks the light from the Sun. But if somehow we could see through the Earth, we would be able to look down at the ground and see the Sun.

Bonus! A list of planets that will not ever block the Sun

There is only one planet that might completely block our view of the Sun and cause you to ask "Where is the Sun?" And there are only two other planets that throw shade on the Earth (Mercury and Venus) because they orbit closer to the Sun than we do.

Here is the list of planets that will never, ever block the Sun:

Mars, Jupiter, Saturn, Uranus, Neptune.

These planets never get between Earth and Sun. They are all further away from the Sun than us. Sometimes these planets go behind the Sun and the Sun blocks our view of them! Think about that for a minute...

Last words of advice about the question "Where is the Sun?"

Still looking for the Sun? It's most likely clouds or night. But, maybe it's one of these objects...

Are your eyelids in the way? Please make sure your eyes are open - eyelids can block the Sun for a long time - even during the day.

Put your hand down - a hand is an effective Sun-blocker.

Are you lying down on a picnic blanket? A foot held up in the air can block the Sun.

So can a person standing above you - ask your friend to move.

Track the Sun with a Sun Tracker

Liked this article? In the next installment of the "Where is the Sun?" series we look at some primitive and scientific tools that you can use to track the Sun.

Comments

John Cummings - June 27, 2018 at 12:17 PM

Nice, especially since it's cloudy today!

starinastar - June 27, 2018 at 12:25 PM

Thanks for the comment, John! This article is a lighthearted look at things that block the Sun, but it can be a gateway into some serious astronomical science.

Pingback: […] solar eclipses and lunar eclipses are […]

Lights All Askew in the Heavens ... But Nobody Need Worry

Sat, 23 Jun 2018 10:53:01 GMT

Lights all askew in the heavens...

New York Times headline about Einstein's theory of the curvature of space time. This hilariously-headlined New York Times article describes the results of the observational experiment performed during the 1919 eclipse. It highlights that the expedition proved Einstein's prediction. But the writer claims that only 12 men on Earth can really understand the result: that light's path is curved by space time. The delightful headline reads:

"Lights all askew in the heavens. Men of science more or less agog over results of eclipse observations. Einstein theory triumphs. Stars not where they seemed of were calculated to be, but nobody need worry. A book for 12 wise men. No more in all the world could comprehend it, said Einstein when his daring publishers accepted it."

Einstein was a theoretical scientist. That means he dreamed up bold theories without direct experimental evidence. His science was one of the imagination. However, in order to succeed in science, a theory must be able to be proven false. So, in 1919 an expedition went in search of observational evidence that would confirm or falsify the prediction of the "bending" of light in spacetime. The adventure was led by Arthur Eddington. They found proof of light's bending rays by measuring the light of a star as it passed the mass of the Sun. The path of the light of a distant star bent in a curve around the edge of the Sun. This result did not falsify the theory and therefore indicated that Einstein's theory was solid. Can you understand space-time as Einstein did? Would you like to understand the ideas of light speed, and the observational reference frame that can speed or slow time?

Reference:

The New York Times scanned newspaper article from 1919. https://timesmachine.nytimes.com/timesmachine/1919/11/10/118180487.pdf

Animal constellations in the night sky. How many are there?

Sat, 12 May 2018 08:50:07 GMT

There are 42 animal constellations in the night sky.

That is almost half of the official 88 constellations! Here are the other types of constellations you will find in the celestial sphere. This is a fun activity for kids astronomy! There are 42 animal constellations, 28 objects, 14 humans, 2 chimeras (a mix of human and animal), and 2 natural features (a river and a mesa).

88 official constellations broken down into 5 groups: 42 animals, 28 objects, 14 humans, 2 chimeras, and 2 natural features. The 88 constellations listed by type:

Animal (42)

Constellation	Meaning	Emoji
Apus	Bird of Paradise	<span style="font-size:6em; line-height:1">🐦🏝️</span>
Aquila	Eagle	<span style="font-size:6em; line-height:1">🦅</span>
Aries	Ram	<span style="font-size:6em; line-height:1">🐏</span>
Camelopardus	Giraffe	<span style="font-size:6em; line-height:1">🦒</span>
Cancer	Crab	<span style="font-size:6em; line-height:1">🦀</span>
Canes Venatici	Hunting dogs	<span style="font-size:6em; line-height:1">🐕🐕</span>
Canis Major	Big dog	<span style="font-size:6em; line-height:1">🐕</span>
Canis Minor	Little dog	<span style="font-size:6em; line-height:1">🐶</span>
Capricornus	Sea goat	<span style="font-size:6em; line-height:1">🌊🐐</span>
Cetus	Sea monster (whale)	<span style="font-size:6em; line-height:1">🐋</span>
Chamaeleon	Chameleon	<span style="font-size:6em; line-height:1">🦎</span>
Columba	Dove	<span style="font-size:6em; line-height:1">🕊️</span>
Corvus	Crow	<span style="font-size:6em; line-height:1">🐦‍⬛</span>
Cygnus	Swan	<span style="font-size:6em; line-height:1">🦢</span>
Delphinus	Porpoise	<span style="font-size:6em; line-height:1">🐬</span>
Dorado	Swordfish	<span style="font-size:6em; line-height:1">⚔️🐟</span>
Draco	Dragon	<span style="font-size:6em; line-height:1">🐉</span>
Equuleus	Little horse	<span style="font-size:6em; line-height:1">🐴</span>
Grus	Crane	<span style="font-size:6em; line-height:1">🦩🏗️</span>
Hydra	Sea serpent	<span style="font-size:6em; line-height:1">🌊🐍</span>
Hydrus	Water snake	<span style="font-size:6em; line-height:1">💧🐍</span>
Lacerta	Lizard	<span style="font-size:6em; line-height:1">🦎</span>
Leo	Lion	<span style="font-size:6em; line-height:1">🦁</span>
Leo Minor	Little lion	<span style="font-size:6em; line-height:1">🦁</span>
Lepus	Hare	<span style="font-size:6em; line-height:1">🐇</span>
Lupus	Wolf	<span style="font-size:6em; line-height:1">🐺</span>
Lynx	Lynx	<span style="font-size:6em; line-height:1">🐈</span>
Monoceros	Unicorn	<span style="font-size:6em; line-height:1">🦄</span>
Musca	Fly	<span style="font-size:6em; line-height:1">🪰</span>
Pavo	Peacock	<span style="font-size:6em; line-height:1">🦚</span>
Pegasus	Pegasus, the winged horse	<span style="font-size:6em; line-height:1">🐴🪽</span>
Phoenix	Phoenix	<span style="font-size:6em; line-height:1">🐦‍🔥</span>
Pisces	Fishes	<span style="font-size:6em; line-height:1">🐟🐟</span>
Piscis Austrinis	Southern fish	<span style="font-size:6em; line-height:1">🐟</span>
Scorpius	Scorpion	<span style="font-size:6em; line-height:1">🦂</span>
Serpens	Serpent	<span style="font-size:6em; line-height:1">🐍</span>
Taurus	Bull	<span style="font-size:6em; line-height:1">🐂</span>
Tucana	Toucan	<span style="font-size:6em; line-height:1">🐦</span>
Ursa Major	Big bear	<span style="font-size:6em; line-height:1">🐻</span>
Ursa Minor	Little bear	<span style="font-size:6em; line-height:1">🧸</span>
Volans	Flying fish	<span style="font-size:6em; line-height:1">🐟🪽</span>
Vulpecula	Fox	<span style="font-size:6em; line-height:1">🦊</span>

Chimera (2)

Constellation	Meaning
Centaurus	Centaur
Sagittarius	Archer

Human (14)

Constellation	Meaning
Andromeda	Princess of Ethiopia
Aquarius	Water bearer
Auriga	Charioteer
Bootes	Herdsman
Cassiopeia	Queen of Ethiopia
Cephus	King of Ethiopia
Coma Berenices	Berenice's hair
Gemini	Twins
Hercules	Hercules, son of Zeus
Indus	Indian
Ophiuchus	Holder of serpent
Orion	Orion, the hunter
Perseus	Perseus, hero who saved Andromeda
Virgo	Virgin

Natural Feature (2)

Constellation	Meaning
Eridanus	River
Mensa	Table mountain

Object (28)

Constellation	Meaning
Antlia	Air pump
Ara	Altar
Caelum	Graving tool
Carina	Keel of Argonauts' ship
Circinus	Compasses
Corona Australis	Southern crown
Corona Borealis	Northern crown
Crater	Cup
Crux	Cross (southern)
Fornax	Furnace
Horologium	Clock
Libra	Balance
Lyra	Lyre or harp
Microscopium	Microscope
Norma	Carpenter's Level
Octans	Octant
Pictor	Easel
Puppis	Stern of the Argonauts' ship
Pyxis (=Malus)	Compass on the Argonauts' ship
Reticulum	Net
Sagitta	Arrow
Sculptor	Sculptor's tools
Scutum	Shield
Sextans	Sextant
Telescopium	Telescope
Triangulum	Triangle
Triangulum Australe	Southern triangle
Vela	Sail of the Argonauts' ship

Comments

John Cummings - May 12, 2018 at 9:06 AM

Learned something new today, didn’t know there were 88 constellations. Thanks Dan!

starinastar - May 12, 2018 at 9:53 PM

Glad you enjoyed the posting! Thanks for the feedback. The stars are the ultimate canvas.

Maddie - October 24, 2019 at 9:51 AM

Only two Chimaera? That is surprising!

starinastar - October 24, 2019 at 12:30 PM

Yes! I agree!! There are so many cool chimerae to choose from. Thanks for visiting. Dan

Pingback: […] Moon is titled toward you, if it’s in an ascending or descending part of its orbit, and what constellation it is […]

Japanese robot will land on the asteroid Ryugu

Sun, 29 Apr 2018 12:26:02 GMT

The Hayabusa2 spacecraft visits the Ryugu asteroid

Update! June 24, 2018 - Haybusa2 has reached Ryuga. See this EarthSky.org article for more information. I just received this wonderful message from a group of students in Japan (thanks to Patricia McGahan for providing the connection!) who are learning and teaching about the Japanese Hayabusa2 mission to the Ryugu asteroid. (Welcome to Japanese language visitors and link to Japanese Wikipedia page.) ようこそ！ここでは小惑星竜口へのはやぶさ2宇宙ミッションについて教えてくれる東京の高校生からの素敵なプロジェクトについてのあなたの情報です。はやぶさ2ミッションのためのウィキペディアのページ。 These Japanese high school students created a board game (in Japanese and English) to teach people about an amazing Japanese spacecraft called Hayabusa2. In June 2018, this Japanese spacecraft will meet up with the asteroid Ryugu, circle it for 18 months, then return to Earth with samples. In addition to observational instruments, the spacecraft has a small explosive material that will drop onto the asteroid! Talk about explosive science!

Explore the TTHS outreach website

The students would like you to explore their website and download the game which takes you through the stages of the mission. The details and links are below. Enjoy!

Hello, Mr. Cummings,

We are Science Club members of TTHS in Japan, the 'Global Challengers' Ms. McGahan teached.

From Science Club of Tokyo Tech High School of Science and Technology(TTHS), let us introduce a hands-on-activity about Astronomy and Space technology we created.

εεε====== ■-OO-■

Project Sugo-Haya2 https://www1.hst.titech.ac.jp/club/sci_club/sugohaya2-e.html

Let's Experience the Round-trip Voyage to the Asteroid Ryugu by the Japanese Explorer Hayabusa2 with a Traditional Board Game 双六 Sugo-Roku.

■-OO-■ ======３３３

We made it so the players can feel the mission of the asteroid explorer which works in a far away space that we even cannot see as well as everyone can enjoy regardless of the age. The game is suitable for two to five players.

This June, Japanese asteroid explorer Hayabusa2 will arrive at the asteroid Ryugu at last. Would you like to experience the Hayabusa2’s mission while playing a fun Japanese traditional board game “Sugo-Roku?"

You can download everything you need to play the game from the link above.

We had McGahan-sensei tell us your wonderful website. We would appreciate it if you could introduce this game in your website. Thank you in advance for your help.

=== Project Sugo-Haya2 produced by Science Club of Tokyo Tech High School of Science and Technology (TTHS) Tokyo, JAPAN

Blue Moon, Dark Moon, Nose Moon, Tail Moon

Mon, 05 Mar 2018 13:34:35 GMT

What is a Blue Moon?

The year 2018 is a Blue Moon bonanza! There was one in January and one on March 31st. The next one won't arrive until October 2020. But, don't worry... we've got 3 other types of moons lined up for you. A Blue Moon. (This image was tinted to make it blue. No, a Blue Moon is not blue.)

The Basics

A Blue Moon happens when there is a Full Moon on the 1st* day of the month and a Full Moon on the last* day of the month. Two full moons in one month! In other words, a Blue Moon is when there is a full moon twice in the same month. These two full moons always happen on the 1st or 2nd and the 30th and 31st of a month. "Blue Moon" is just a name for the second moon in that month - the moon does not turn the color blue. Read on to learn about how the Blue Moon came to be and some suggestions for giving the other moon phases "Blue Moon" style names when they appear twice in a month. Suggestions are: Dark Moon, Nose Moon, and Tail Moon.

A month is just a name for 30 or 31 days in a row

Month came from the word Moon. The concept of the month came from the moon phase cycle. It is not a coincidence that the month is about as long as a moon phase cycle. They are related. The Blue Moon not a very old concept... it was invented by accident in 1946. It happens because our 12 month calendar no longer matches the moon phases. The moon's phases have a cycle that is 29 and a half days long. All calendar months (except February) are 30 or 31 days long. So, every once-in-a while ("once in a blue moon" you might say) the moon's phase cycle fits inside a single calendar month. What is a Blue Moon? When the moon phase cycle fits into a month. Here's a calendar month showing the 2 full Moons that will happen in October 2020. October 2020 will have a Blue Moon because there are 2 Full Moons in the month.

Evolution of Blue Moon definition.

Today, the definition is: "A Blue Moon is the second full moon in a calendar month." Before 1946, this was not the meaning of "Blue Moon." Most years have 12 full moons in the year. But, sometimes there are 13 full moons in a calendar year. In the "olden days," it is thought that the term Blue Moon was a way of naming the "extra" 13th full moon that sometimes comes in a calendar year. This naming of the extra moon in a year was handled by calendar makers (people who picked the calendar dates for holidays like Easter and Passover). Normally, this "Blue Moon" (old style) was thought of as the 4th full moon in a season (normally only 3 full moons are in a season). This linguist thinks it was really just a funny saying to mean something like "when pigs fly" as in "when the moon turns blue" (which according to word history research is something that people believed would never happen).

A Blue Moon that's not a Full Moon

The blue moon refers to the full moon phase. The fact that the entire moon phase cycle fits into a 30+ day calendar month is interesting. But, it's just a phase. And the other moon phases are arguably much more interesting. Think about it for a second... it's not just the full moon that can appear twice in one month. Any of the other major phases can appear twice in one calendar month. Why should the Full Moon be the only phase with a special name? The full moon is just the most obvious and well-known phase. It is also the easiest to spot because it is so bright! However, there are 3 other major phases of the phases of the moon (new, first quarter and last quarter). Those phases can appear twice in a calendar month just like the full moon phase. For instance, October 2018 will have two "Last Quarter" moons, one on October 2nd, 2018 and one on October 31st, 2018. This Last Quarter phase should have its own special name too. I think that we should call the 2nd last quarter moon in a month the Nose Moon. October 2018 will have a "Nose Moon" - it's like a Blue Moon but with Last Quarter moon instead.

Blue Moon extended: Dark Moon, Nose Moon, Tail Moon

Blue moons are fun to think about! It's when the wall calendar overlaps with the physical motions of the Moon and the Sun and two full moons happen in the same calendar month. There are also other phases the "happen twice" in a calendar month. These phases should also have names. Blue Moon -2 Full Moons - already in widespread use, common name. Here are new names I created to give the other moon phases some glory too:

Dark Moon - 2 New Moons - New moons are dark and cause eclipses.

Nose Moon - 2 Last quarter -the last quarter moon leads us in our orbit.

Tail Moon - 2 First quarter - this moon trails Earth by about 4 hours.

What do you think of these new names? Leave a comment below.

Summary

The simplest and shortest definition is: Blue Moon is the second full moon in a month. The Blue Moon used to mean something slightly different relating to the adjustments needed to keep lunar and solar calendars in synch: the 4th full moon in a normally 3 moon season. The Full Moon phase is only one of the 4 major phases of the moon - we should have names for all moon phases when they appear twice in a calendar month. Full = Blue Moon, New = Dark Moon, Last = Nose Moon, First = Tail Moon.

Fun Facts

February can never have a Blue Moon because it only has 28 (or 29) days and the Moon becomes full every 29.5 days. The Blue Moon got its modern meaning because of a mistake by one of the writers in Sky & Telescope magazine in March 1946. There are historical records that tell us that Volcano dust and forest fires can cause the Moon to appear the actual color blue.

Notes

* The first full moon can be on the 1st or the 2nd day of the month, and the last full moon can be on the second-to-last or last day of the month.

References

Wikipedia page on Lunar Phase

Comments

mark winkel - June 9, 2019 at 11:40 PM

What is up with the moon tonight, june 9th 2019? Its a half moon that appears to have a second glow to it, like a watermelon rind, it is bright and is notched on the top and bottom. It looks like there is the half moon with a dark line on the curved side, and a bright, thick rind on the curved side ( may be 1/4 as thick as the half moon). The "rind does not make it all the way up to the flat side of the half moon ( thus the notchef look to the rind). Sky was clear, no clouds.

starinastar - June 9, 2019 at 11:55 PM

Hi Mark! The description you shared sounds really interesting. I only saw the half moon shape tonight. It reminded me that we have a double new moon coming up in August 2019. A new moon will happen on the 1st and the 30th of August this year. I call that second one the dark moon after the tradition of naming two full moons in one month the blue moon. Cheers! Dan

Astronomy Koan

Fri, 02 Mar 2018 09:44:54 GMT

Astronomy Koan - Definition

A family views the visible orbit path of the earth. An astronomy koan is a short, easy-to-memorize phrase that distills a key teaching about astronomy (especially physical astronomy). The words are simple enough for a child to learn, but they carry complex insights about scientific observations. The astronomy koan is a mnemonic that has layers of meaning or presents an ambiguous or challenging observation in a pithy phrase. Try memorizing one of these - you can bring these with you everywhere.

Four Physical Astronomy Koans

That star rose earlier today.

The moon moves toward the dawn.

Night is where you are.

Same Sun all night. Dusk to the left, dawn to the right.

What do you think about these? Do you know any astronomy koans? Share your ideas in the comments section.

Merry-Go-Round Earth shows Seasonal Constellations

Mon, 26 Feb 2018 16:20:54 GMT

The Earth is like a Merry-Go-Round

A Merry-Go-Round is a good model of daily Earth rotation.

The Earth is like a merry-go-round showing us seasonal constellations

That iconic childhood ride. Round and round each day we go, round and round each year we go, where we stop nobody knows! When we look out from the edge of the ride we can see the space beyond. Sometimes the Sun occupies that space, and sometimes that space is the night sky filled with stars.

The Sun is like a campfire

The central blaze, the outdoor hearth, the gathering place. It draws us like moths to the flame. We circle it, center our attention on it, we turn away from it to warm our backs, then we turn to face it again. It teaches us, it warms us, its memory runs deep in our collective mind. On our path around the Sun we keep a good distance away because it is hot, but we always stay nearby because if we move outside its warmth we will freeze in deep space. People standing around the Camp Winnebago campfire. Image credit: Daniel Cummings

The stars are like points of light placed on a giant spherical dome

That dome of stars encloses the Sun and the Earth. They surround us completely as if we are floating at the center of a gigantic sphere. The stars do not move*. A star globe showing the stars as if they are painted on the sky surrounding the Earth. Image from World Globe Universe.

Riding a merry-go-round that turns once a day

Imagine riding on a merry-go-round (it moves once per day in a counter-clockwise direction). Imagine that the merry-go-round is next to a campfire. You can look out from the edge of the merry-go-round and see the campfire some of the time, but you can't see the campfire all the time because you cannot look across the middle of it. Each time the merry-go-round turns you see the campfire get closer and then you pass it and eventually the fire is no longer visible as you get carried away by the merry-go-round and turn away from the campfire. While you are turned away from the campfire, you do not see any light from the fire. You are looking away from the campfire into the night - you see the stars beyond.

A merry-go-round near a campfire under a dome of stars.

These three parts of the seasonal constellation model can help us understand why we see different stars on winter nights than we do on summer nights. Why do we see different constellations at night during different seasons? We see seasonal constellations because the night sky that is visible from the Earth changes over time. It shows us a slightly different view of the stars each day. As you turn away from the Sun (campfire), you cannot see the Sun (campfire) anymore, but you can see the space beyond - and the stars and constellations that fill that space.

Models of Earth and Sun

To help us understand, we will build a physical model of the Sun as a campfire and a physical model of the Earth as a merry-go-round circling that campfire. In our Physical Astronomy model the campfire is the Sun and our bodies are the merry-go-round Earth. We will spin day after day on the daily merry-go-round. We started with one merry-go-round to model the day, but the Sun itself is a second, bigger merry-go-round that carries the Earth around once a year. These two merry-go-rounds work together to present the ever-changing seasonal constellations. We show this idea below in an image.

The campfire is the Sun, we are the Earth

In this physical model of our solar system, the campfire will be the Sun. Our bodies will be the Earth. Our movements will be like the merry-go-round. We can face the campfire or we can turn away from it.

Looking "up" means looking "out" - into space

When we turn to face the campfire and look at the campfire (the Sun) our faces are like the people on the day side of the Earth. People on Earth look "up" during the day and see the Sun. When we turn away from the campfire our faces are like the people on the night side of the Earth. We look "up" and see the stars out in space. A model of the Sun and Earth. The campfire is the Sun and the person is the Earth.

Day = face toward the Sun, Night = face away from the Sun

The Earth has two sides - the day side and the night side. Half of the Earth is always in daytime and half of it is in night. Round and round the Earth rotates each day like a merry-go-round. This merry-go-round never stops. Half of the time we are facing the Sun and half of the time we are not. We call the side that faces the Sun (the campfire) the day. All the people there can see the Sun "up" in their sky. As the Earth spins it carries people from the night side into the day side and they experience sunrise. We call the side that faces away from the Sun (the campfire) the night. All the people there can see the stars "up" in their sky. As the Earth spins it carries people from day into the night side and they experience sunset. Spinning and spinning each day, the Sun and other sky objects above us seem to move into view and then disappear out of view. This is because the merry-go-round Earth carries us around each day and we see a new view of the space around the Earth. The Earth is like a Merry-Go-Round. It carries us around and around each day.

Two motions, Two Merry-Go-Rounds - Daily and Yearly

The Earth moves in two ways as it circles the Sun: daily and yearly. You can think of these two motions like a smaller merry-go-round (daily) being carried along on a bigger merry-go-round (yearly). A Merry-Go-Round on a Merry-Go-Round. The Earth spins 365 times in one Earth year.

Daily - the smaller merry-go-round

As we learned earlier, our Earth's daily motion is to spin, to rotate. The Earth carries us once-a-day on a merry-go-round ride. As we work, play, eat, and sleep on the surface of the Earth, it carries us under and then away from the Sun. During the day we face the Sun (from dawn to day's end), then we are carried away from the Sun (from sunset to night's end). As you think about this idea you begin to realize that night is where you are more than what time it is.

Yearly - the bigger merry-go-round

Our yearly motion is to orbit, to revolve, to follow a path around the Sun. It takes the Earth one year to complete this path. It takes 365 days, 365 small merry-go-round turns to travel the entire yearly orbit of Earth around the Sun. As we learned earlier, one side of the Earth is always facing the Sun, this side of the Earth is always day. Throughout the entire year, one side of the Earth is always day, and one side is always night. There is always daytime somewhere. Fun Fact: If you could fly in a plane for a year at the same speed the Earth is rotating, you could stay on that daytime side and experience continuous daytime!

Seasonal constellations - the night sky changes during the year

As the Earth follows its yearly path in orbit around the Sun (the campfire), the stars in the night sky change. We see winter, spring, summer, and fall constellations in yearly rhythm. Why does this change of seasonal constellations happen? Let's go back to the two merry-go-rounds. Our small merry-go-round is turning quickly like the day. The bigger merry-go-round is turning slowly as the year. The day merry-go-round spins 365 times a year. So, every year, the small merry-go-round gives us 365 views of the night sky! Every day on our small-merry-go-round we see the daytime sky and every night we see the night time sky. At night (facing away from the Sun) we are able to see the stars. This image shows how we are able to see different views of the star dome (in this case the zodiacal constellations) as the Earth goes through its orbit. In January, Gemini is visible at night. In May, Libra and Scorpio are visible at night. Seasonal Constellations - image provided courtesy Louisville University Physics Department under Creative Commons license.

We can't see stars during the day, but they are there!

However, during the day there are other stars in the sky but they are not visible because the Sun is too bright. We cannot see those seasonal stars and seasonal constellations in the night sky until the bigger merry-go-round carries us further along the yearly path. The Earth moves along the yearly path and each night stars seem to move higher and higher in the eastern sky. As we move on this bigger merry-go-round our view of the night sky changes slightly. Each day as we look "up" into space at night, we are looking away from the Sun. And each day the Earth moves a little bit further along on its yearly path. Eventually, as the bigger merry-go-round carries us around in half its yearly motion, the night sky will show us a completely different set of stars. 6 months from now, the stars will be completely changed in the night sky! We will see a different set of seasonal constellations.

Summary

The merry-go-round is a good model that can help us understand the daily and yearly motions of the Earth. We used the campfire as a model of the Sun. We learned how to imagine the stars painted on a giant sphere with the Earth at the center. This idea of a star sphere is a simplification, but it helps us to understand how seasonal constellations change over the year. As part of the model, we use our bodies to become the Earth and experience day and night by spinning and traveling the yearly Earth orbit path. We also learned that when we are looking "up" into the sky, we are actually looking "out" into space.

Science background and terms

Daily Earth motion is called rotation on an axis. Yearly Earth motion is called orbit. * Stars do move, but only very slowly - it is called "proper" motion. Seasonal constellation changes are caused by "sidereal" motion.

Comments

Jim - March 1, 2018 at 5:25 PM

Nice analogy. One thing that kind of blew my mind when I realized it is that we don’t just see half the starry sky each night (ie not just the parts behind an extension of the day/night line on the earth in your blue zodiac circle), but actually we see all but about a quarter of the sky-sphere (since the horizon is a tangent from earth, with stars visible an hour or so on the dark side of each terminator). Of course, for most people, it’s what’s up at mid-evening that matters....and that sure does wheel around month to month.

starinastar - March 1, 2018 at 6:51 PM

Yes! We get a generous tour of the sky every night... if we are willing to stay up late. But, as you observed, it's really the stars that are out in the early evening that make the most impact. I like that: "the horizon is a tangent from the earth." I've got an article in draft discussing "how far we can see" under many conditions. I love showing kids the Andromeda galaxy! It's so far away and the light is unimaginably old. It makes a huge impression. Jim, I'll be giving this presentation this Saturday March 3rd, 2018 in Croton-On-Hudson, NY. Thanks for the observations on the write up!

Stellarium - Find the Humanity Star

Thu, 15 Feb 2018 19:06:40 GMT

A new satellite called the Humanity Star looks like a disco ball

Update Apr. 1, 2018. The Humanity Star is no longer an active satellite – it has fallen out of the sky: https://www.theverge.com/2018/3/22/17144208/rocket-lab-humanity-star-satellite-new-zealand-astronomy However, even though the Humanity Star is now gone, this article still teaches you how to load satellites into Stellarium. So, read on for a quick tutorial on how to track any satellite in Stellarium. Looking for information on how to track the Humanity Star any satellite location using Stellarium astronomy software? Here is a quick tutorial on how to find the Humanity Star any satellite using Stellarium. The Humanity Star satellite before launch - still on the Earth. Rocket Lab founder and CEO Peter Beck announced that the company's rocket had placed a special satellite in a 90 minute orbit around the Earth. A lot of people want to see this new "star" in the sky. Stellarium can help you do that. If you don't have Stellarium, you can download a copy here. And I have a few tutorials that can help you get started with this amazing piece of software.

Tutorial - use Stellarium to find the Humanity Star satellite

First, you have to use the satellite database which is available in the Configurations > Plugins section of Stellarium. Click on the wrench with the star, then click the Plugins tab, then scroll down until you see "Satellites" in the list on the left. Stellarium configuration window showing the satellites plugin.

Update the satellite data

Once you have done that (be sure to check "Load at startup" you will have a list of satellites to choose from. However, there are new objects launched into space every day, so this plugin has a button that says "Update Now" Update the satellite list to get all the newest satellites - including the Humanity Star.

Search for the Humanity Star

Now, open the Search panel in Stellarium and type Humanity Star and hit the return key on the keyboard or click the magnifying glass button. Open the Search panel and type Humanity Star. Stellarium will find it. Stellarium will highlight the Humanity Star. Hit the space bar to lock it into the view.

Time lapse

Now that Stellarium has locked the Humanity Star into the view center. You can speed up time by tapping the "L" key on the keyboard a few times. This will speed up the clock and show you where the Humanity Star is traveling in the sky. Stellarium Humanity Star in the Constellation Cygnus in March 2018 as seen from the New York Metropolitan Area.

Location, Location, Location

Editor's Note: In the comments below, a visitor (thanks, Hector!) - who used these instructions to successfully find the object - says that you should try to establish a very accurate location in Stellarium. You should do this before locking in on the positioning and tracking of the Humanity star. I completely agree! Make sure you use the "Location window" to enter your exact latitude and longitude - this will be helpful for all observations in Stellarium, but will be especially important with a low earth orbit object like the Humanity Star.

Predicting the brightness (magnitude) of the Humanity Star

By using this website, you can enter your location on Earth (in the top right of the page choose Location) and track many satellites and get predictions for when they will fly overhead. The Humanity Star is one of several "satellites of special interest" so you can click on the link and see flyover predictions with magnitude estimates. According to the satellite tracking website "Heavens Above" the Humanity Star is not one of the brightest objects in the sky. In the second week of March 2018, it ranges from magnitude 4.1 to 8.4. Magnitude 4.1 is just barely visible to the naked eye in light polluted suburban skies, but magnitude 8.4 is basically invisible under all normal viewing conditions. Table of predictions for the New York metropolitan area Humanity Star visibility and brightness. I would love to hear if you were able to use these directions to find and see the Humanity Star in your area! Clear Skies. Happy Humanity Star satellite hunting with Stellarium.

Comments

Pingback: […] Hello! Are you looking for information on how to use Stellarium to find the Humanity Star satellite? It’s your lucky day! Click here for a tutorial that teaches you how to find the Humanity Star satellite with Stellarium. […]

Hector - March 14, 2018 at 6:12 AM

I struggled to find the Humanity Star on the sky for several months, until last Sunday (March 11th 2018), when I finally saw it (from Blaasveld, Belgium), all thanks to your directions! I installed the Stellarium, which I do agree is an amazing piece of software, followed the instructions, and there was the Humanity Star almost touching one of the Ursa Major stars (Phecda) at 19:46:19 of that day as predicted! It was shinny enough that night, visible to the naked eye even when the sky was not yet fully dark. It cruises across the sky rather fast, so it is easy to miss or to take for a high-flying plane, and the Stellarium gave a good idea about the speed, time, path and location relative to know stars or constellations. One important thing is to enter your location as accurate as possible (use a GPS or get coordinates from Google maps); do not use e.g. the location of the center of your city, as that will introduced a small (but visible) error in the trajectory or position of the Humanity Star. The second most important thing: be on time and use an accurate clock! The Stellarium allowed me to identify a second satellite (USA 186) that passed just about 1 second later, following a rather close path.

starinastar - March 14, 2018 at 7:42 AM

Hello Hector! I am glad to hear your observation was a success. And thank you for the suggestion about getting very precise location established. I will add your suggestion to the article. I found it surprising how dim the object was reported to be by the heavens-above tracking site. However, it sounds like you had no difficulty finding it after the position was shown in Stellarium. Daniel

Naus - April 1, 2018 at 6:54 PM

I could find the humanity star with stellarium a while back but now I'm surprised I seem to be unable to find it anymore in despite I have checked all the available source to update the satellite plugin, anyone else has the same issue?

starinastar - April 1, 2018 at 10:08 PM

Hello Naus! Glad to have you here. It looks like the latest Satellite catalog in Stellarium has dropped the object from the listing. The Humanity Star is no longer an active satellite - it has fallen out of the sky: https://www.theverge.com/2018/3/22/17144208/rocket-lab-humanity-star-satellite-new-zealand-astronomy

Quiz - Can we see the Sun at midnight? Where is the Sun?

Tue, 13 Feb 2018 22:49:15 GMT

Can we see the Sun at midnight?

Yes. We can see the Sun at midnight. But, only if we are at one of the polar regions during the Summer season.

A quiz - seeing the Sun at midnight - don't scroll til you try to answer!

When you see the Sun "rising" in the morning at dawn you are facing the east. When you see the Sun "setting" at the end of the day you are facing the west. Assuming you are not above the Arctic circle and not too close to the equator... if you could look right at the Sun (when the night is exactly half over) - by looking through the Earth - which cardinal direction would you be facing? East, West, North, or South? A compass rose showing the cardinal directions.

Answer and Explanation

This quiz tests an observer's ability to think about cardinal directions at the same time paying attention to meridian, time, and hemispherical location. When we see the Sun "rising" in the morning at dawn we are facing the east. When we see the Sun "setting" at the end of the day we are facing the west. When we look at the Sun at noon in the northern hemisphere we are facing south. SPOILER ALERT -- And when we look at the Sun - as if the Earth were transparent - at midnight in the northern hemisphere we are facing north. In the southern hemisphere sunrise and sunset appear in the same cardinal directions (East and West). But as we pretend that we can look through the Earth at the Sun... at midnight... we are facing south. See the diagram below. I welcome any and all observation and feedback on this quiz! Contact me by clicking the blue bubble in the bottom right of this page.

Comments

Pingback: […] the Sun (from sunset to night’s end). As you think about this idea you begin to realize that night is where you are more than what time it […]

Irving - May 12, 2018 at 10:15 PM

I learned a lot from this quiz about the Sun at midnight. I am really trying to imagine looking "through" the earth and it is difficult for me. Do you have any tips?

starinastar - May 19, 2018 at 1:02 PM

Hi Irving! Thank you for the comment and helpful feedback about learning to see the sun at night. The main thing to remember is that we are on the surface of a spinning globe. Try to imagine if that globe became see-through and you were able to see all the way through to the other side! If you look through the earth as if it were made of glass you would see the Sun. Hope that helps you understand how to see the sun at night.

"Star In a Star" Translated into 90 languages

Thu, 08 Feb 2018 18:26:59 GMT

Translation of Star In A Star Physical Astronomy articles

Would you like to learn how to say the word "star" in languages that are not your own? All of the articles about Physical Astronomy here at Star In A Star can be automatically translated. This amazing Google Translate widget lets you choose any language.

Google Translate widget can be used to translate these articles into any language.

Try it out! If you are on desktop ... click the link at the top right to translate. If you are on mobile, click the translate widget at the bottom of the page.

For a bit of fun today... Here is a list of languages and the phrase "Star In A Star" in that language. I particularly like the languages where the word "star" changes slightly if it is inside another star (in Bosnian: zvezda u zvezdu). Also, I am fond of non-roman script languages - just for how beautiful they look ( this is Lao: ດາວໃນດາວ ).

Afrikaans: ster in 'n ster

Arabic: نجمة في نجم

Azerbaijani: bir ulduzda ulduz

Belarusian: зорка ў зорцы

Bulgarian: звезда в звезда

Bengali: একটি তারকা তারকা

Bosnian: zvezda u zvezdu

Catalan: estrella en una estrella

Cebuano: bituon sa usa ka bituon

Czech: hvězdička ve hvězdě

Welsh: seren mewn seren

Danish: stjerne i en stjerne

German: star in a star

Greek: αστέρι σε ένα αστέρι

English: star in a star

Esperanto: star in a star

Spanish: estrella en una estrella

Estonian: star täht

Basque: izar bat izar batean

Persian: ستاره در یک ستاره

Finnish: tähti tähteä

French: étoile dans une étoile

Irish: réalta i réalta

Galician: estrela nunha estrela

Gujarati: સ્ટારમાં તારો

Hausa: star a star

Hindi: स्टार में स्टार

Hmong: star in a star

Croatian: zvijezda u zvijezdi

Haitian Creole: zetwal nan yon etwal

Hungarian: csillag egy csillagban

Armenian: աստղ աստղում

Indonesian: bintang di sebuah bintang

Igbo: kpakpando na kpakpando

Icelandic: stjörnu í stjörnu

Italian: stella in una stella

Hebrew: כוכב בכוכב

Japanese: 星の星

Javanese: bintang ing sawijining bintang

Georgian: ვარსკვლავი ვარსკვლავი

Kazakh: жұлдызға жұлдыз

Khmer: តារាក្នុងផ្កាយ

Kannada: ನಕ್ಷತ್ರದಲ್ಲಿನ ನಕ್ಷತ್ರ

Korean: 스타의 스타

Latin: star in a star

Lao: ດາວໃນດາວ

Lithuanian: žvaigždė žvaigždė

Latvian: zvaigzne zvaigznīte

Malagasy: kintana amina kintana

Maori: whetu i roto i te whetu

Macedonian: ѕвезда во ѕвезда

Malayalam: ഒരു നക്ഷത്രത്തിൽ നക്ഷത്രം

Mongolian: одтой од

Marathi: तारा तारा

Malay: bintang dalam bintang

Maltese: star fi stilla

Myanmar (Burmese): ကြယ်အတွက်ကြယ်ပွင့်

Nepali: स्टारमा तारा

Dutch: ster in een ster

Norwegian: stjerne i en stjerne

Chichewa: nyenyezi mu nyenyezi

Punjabi: ਸਟਾਰ ਵਿਚ ਸਟਾਰ

Polish: gwiazda w gwiazdce

Portuguese: estrela em uma estrela

Romanian: stea într-o stea

Russian: звезда в звезде

Sinhala: තරුවක තරුවක

Slovak: hviezdička v hviezde

Slovenian: zvezda v zvezdi

Somali: xiddigta xiddig

Albanian: yll në një yll

Serbian: звезда у звезду

Sesotho: naleli linaleli

Sundanese: béntang di béntang anu

Swedish: stjärnan i en stjärna

Swahili: nyota katika nyota

Tamil: நட்சத்திரத்தில் நட்சத்திரம்

Telugu: స్టార్ లో స్టార్

Tajik: ситораи дар ситора

Thai: ดาวในดาว

Filipino: bituin sa isang bituin

Turkish: bir yıldızla yıldız

Ukrainian: зірка у зірки

Urdu: ایک ستارہ میں ستارہ

Uzbek: yulduzli yulduz

Vietnamese: sao trong một ngôi sao

Yiddish: שטערן אין אַ שטערן

Yoruba: Star ni irawọ kan

Chinese: 明星在一个明星

Chinese (Simplified): 明星在一个明星

Chinese (Traditional): 明星在一個明星

Zulu: inkanyezi kwenkanyezi

Comments

Mimi Howards - May 19, 2018 at 10:26 PM

Very nice. Thank you for providing these translations.

Physical Astronomy - Definition of a New Way of Teaching

Sat, 27 Jan 2018 19:58:43 GMT

Definition of Physical Astronomy

Vitruvian Man with Moon Phases Physical Astronomy is a new way of teaching astronomy that emphasizes the human body and its relationship to other moving objects in space. The goal is to bring geometric and scientific awareness to a child's everyday sky observations. Kids learn easily visible sky motions at a "kid's eye level."

The Sun does not move... we move

One of the first steps in Physical Astronomy is to forget you ever heard the words "Sunset" or "Sunrise." These words (while rife with history, beautiful in their own right, and descriptive) are scientifically wrong. These words obscure the truth of our trip around the Sun. We are on the Earth, the Earth is spinning; the Sun appears to be moving, but it is us moving. From the outset Physical Astronomy challenges you to reconsider long-held perceptions. It challenges you to trade them for curiosity, scientific thinking, and observation.

Foundations of Physical Astronomy

Physical Astronomy means learning basic astronomy concepts with a Kinesthetic approach: your body is on the Earth but traveling in space. While we are actually traveling in many directions at the same time the daily perception of our direction is of traveling "under the sun." Through imagination and knowledge, you can see your place within the motions of the Earth, Sun, Moon, stars, and galaxies. Science and the Scientific Method are the foundations of Physical Astronomy. Teaching methods, tools, and models scale Astronomy concepts to human size. Imagination transports us beyond our current understanding.

The Future of Physical Astronomy

I would like each child to get a little bit closer to understanding advanced but fundamental physical concepts like light speed, orbits, phases, star distance. The goal is to offer very early involvement with physics and motion. This early exposure to the idea of the speed of light can give a future adult a natural base of understanding. For most of human existence we earthlings did not know that we lived on the surface of a giant sphere. My goal with this new way of teaching astronomy is to bring curious young minds fun, high-quality, experiential, developmentally tuned lessons for getting involved in the process of scientific discovery. My intent is to build a strong and scientifically accurate conceptual foundation in a child's mind. This will bring a passionate and articulate dedication to astronomy specifically, and science in general. We will cover these topics and more: the earth, moon, sun, planets and stars, black holes, asteroids, astronomy versus astrology, visible light versus invisible energy, other celestial bodies like comets, neutron stars, pulsars, quasars, radio waves in multiple frequency bands, telescopes, dark matter and dark energy, and ultimately space (everything outside the earth atmosphere), and the history of astronomy.

The next Halley, Herschel, Hubble, Einstein, or Hawking.

I have always been captivated by the sky. And I’ve come to realize that even though everyone has some knowledge of what’s “up there” (no matter how much absolute knowledge someone possesses) they always want to know more. The study of the sky is endless! There are so many ways to bring that sense of depth to more and more kids. Let’s continue so that we nurture the development of our next Halley, Herschel, Hubble, Einstein, or Hawking. I have a big goal with my Physical Astronomy education programs: to encourage people to see the world from a new perspective and to transform them. We do this by offering repeatable experiences - personal science experiences - that shape the way we perceive our particular place in the universe.

Comments

Jim - March 1, 2018 at 5:13 PM

Excellent statement of purpose!

starinastar - March 1, 2018 at 6:24 PM

Thank you for the kind words, Jim!

Moon Phase Emojis - A Review

Wed, 24 Jan 2018 18:06:38 GMT

Moon Emojis - and other space emojis

Emoji designers created a nice range of moon emoji, astronomy emojis and space emojis. My favorite emojis are the Moon Phase Emojis.

Here are the moon emojis, astronomy emojis and space emojis as real emojis that can be selected individually (or in groups) and copied. These look different on each browser. The moon emoji is my personal favorite.

New for 2019! Saturn and Astronaut emojis:

Earth globe emojis:

Moon phases emojis in order — full moon to new moon to full moon:

Moon, Sun, and Star emojis:

Explosion, Comet, Sun, and Rainbow emojis:

Spaceship and Satellite emojis:

Alien and Space Invader emojis:

Map, Otsukimi (お月見), Sunrise, Sunset, Shooting Star, City Skylines, and Milky Way emojis:

Astronomy Tools — Telescope emojis:

Religions with Moon and Stars emojis:

Abstract Sun, Earth, Galaxy, Star, and Full Moon emojis:

Horoscope / Zodiac / Astrology emojis — Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, Pisces, Ophiuchus:

Miscellaneous Space Symbol emojis:

Note: There is currently no official lunar eclipse emoji, nor is there a solar eclipse emoji. Until the emoji designers create real eclipse emojis, I suggest using the black versions of the Moon and Sun. Use <span style="font-size: 1.8em;">☾</span> for a lunar eclipse (it doesn't look like any Moon phase — it actually somewhat resembles an eclipse) and <span style="font-size: 1.8em;">☀</span> for a solar eclipse emoji — because the black spot with lines looks like a total solar eclipse showing the Sun's corona.

Here is a screenshot of all of the moon emoji and space emojis as seen on Apple's Mac "High Sierra" OS. Bonus: this list shows the moon phase emojis in order — the correct order of the phases of the moon.

Emoji Variations

Did you know that emojis look different depending on which type of device you are seeing them on?

Here is what the Full Moon Emoji looks like on Apple Macs:

The Full Moon emoji as seen on Mac Computers

And here is what it looks like on Microsoft PCs:

The Full Moon emoji as seen on Windows PCs

References

Emojipedia has a catalog of all the variations of emojis including the Full Moon Emoji

See Mercury and Venus orbits during the day

Sun, 07 Jan 2018 17:19:07 GMT

Your hands and arms help you see the orbits of Mercury and Venus and the shape of solar system

Question: If you could see the orbit of Venus would it fill the whole sky? The answer might surprise you! You can use your hands and arms to see the size of the orbits of the solar system's inner planets: Mercury and Venus. Imagine (as pictured below) if the orbit of Mercury were visible as a red oval and the orbit of Venus were visible in green. Two hand spans show the orbit of Mercury, elbows show the orbit of Venus.

Physical Astronomy - see Mercury and Venus orbits

Caution! Do not look directly at the Sun without proper solar safety glasses on. Turn toward the Sun, hold your arms out straight, hands up in the air with fingers spread wide and thumbs touching. Your pinky fingers now span the width of the orbit of Mercury and your elbows span the width of the orbit of Venus. Both of the entire orbits of Mercury and Venus orbits would be visible in the sky all at once - if they could be made visible during the day.

See The Orbit of Mercury - Aldebaran to Pollux

Mercury's orbit seen against the background of springtime evening stars. Stellarium view. At night, you can use stars to help visualize the size of the inner planet's orbits. To visualize that in the night sky (in springtime) Mercury's orbit spans from Aldebaran to Pollux. Astronomers use "hours" to measure east to west sky movement. Mercury's orbit spans 3.5 hours.

See The Orbit of Venus - Regulus to the Pleiades

The orbit of Venus seen against the background of springtime evening stars. Stellarium view. Venus's orbit spans 7 hours of the sky. To visualize that in the night sky (in springtime) Venus's orbit spans from Regulus to the Pleiades (the seven sisters).

Summary

We answered the question: If you could see the orbit of Venus would it fill the whole sky? The answer is no, it would fill only part of the sky. We learned a Physical Astronomy technique for how to see the orbits of the two inner planets Mercury and Venus.

Comments

John Cummings - January 7, 2018 at 5:31 PM

Nicely done. Perhaps you could define an ‘orbit’ for the younger children? Also, have the’details’ fields fill in automatically for fans who’ve previously posted. Probably would increase the number of comments? Keep those posts coming!

starinastar - January 7, 2018 at 10:09 PM

Thanks for the feedback. That's one of the hardest things about teaching these concepts to a wide range of ages - it's also one of the most challenging and fun aspects too. Orbit means flying around in a "circle" around something bigger. I'll look into a way to avoid making you type your email each time - that's a good idea!

Jim - March 1, 2018 at 5:08 PM

Image of venus orbit is shown a hour or two (ie 2-4 sun-travel weeks) off, compared to stellar signposts noted....shown extending from Cancer out toward Aries). I get that you’re trying to use the same sun-point, but it’s confusing to not find Regulus in the image.

starinastar - March 1, 2018 at 6:22 PM

Aha! Good catch. I will regenerate a more accurate image that matches the text of the article. Thanks Jim!

Shapes with Shadows - astrosketching Moon features with Alex Massey

Mon, 01 Jan 2018 15:08:46 GMT

Shapes with Shadows – what they can tell us

This the first of two special guest posts by Australian astrosketch artist Alexander Massey

Live View Sketch of Moon craters Azrachel, Alphonsus, and Ptolemaeus by Alex Massey

Ptolemaeus, Alphonsus, and Arzachel... the names of three massive, interlocking craters on the Moon. These three craters tell the story of the ancient Moon's creation and evolution. It's a story of violent bombardments and oceans of lava. We can use light and shadows to reveal the shapes and deep history of these features.

Most people think of astronomy a science of light. But, light creates shadows when it hits things. Those features that lie in the shadows, the dark parts and seemingly just-in-the-way-of-the-light parts, are just as important as those that shine brightly. These dark shadows form most of the mass of all galaxies, house stellar nurseries, reveal old lava rivers on the Moon, and create curious plays of light and dark. These can play tricks on our eyes and make patterns appear. Shadows hide stories in their inkiness.

I have sketched at the eyepiece many of these dark shapes, and while shadows might just seem to get in the way, in reality they give shape to the light.

Shadows on the Moon

Our closest neighbour, the Moon, holds many secrets that lie in the shadows. As the Sun rises over the lunar horizon, it casts shadows that tell stories that are billions of years old. The lunar surface is a layered pattern - a palimpsest - that we can learn to interpret.

The Sun rises and sets across the Moon's surface. Over the course of a month on Earth, we see this as the phases of the Moon. The \u201cterminator\u201d on the Moon is the boundary of those phases. It marks the transition from dark to light. Exploring the terminator, even with a small telescope, allows you to discover many of the Moon\u2019s secrets.

Even with a modest telescope, you can see a lace-like network of fine lines or cracks that resemble crazing (as seen in some glazing of pottery). It is only while the Sun is shining at a very shallow angle that these typically shallow lines show themselves. Yet the origins of these fine lines is quite varied.

The Moon's history told in shadows

Four billion years ago when the Moon was very young, its interior was very hot and molten. Its surface had a thin crust. In many ways just like the Earth today, but without the atmosphere and oceans of water. The thin crust was easily pierced by large asteroids, allowing molten lava to pour into and flood the crater. When the Moon was young and very hot, these craters always totally filled in with lava.

Move to three and a half billion years ago, the Moon cooled, the crust got thicker, and it was both harder for large asteroids to pierce through the crust and lava filled in less of the crater. Eventually, three billion years ago, the Moon cooled to the point where lava no longer flowed, and impact craters no longer filled with lava.

We can see the ages of the craters by understanding what the shadows cast across them mean; their morphology reveals their history.

A walk on the Moon... with our eyes

Let's go for a walk on the Moon. We can't yet visit there ourselves but we can tour the moon's surface with our eyes. The trip will take us to the 3 craters we mentioned earlier.

Live View Sketch of Moon craters Azrachel, Alphonsus, and Ptolemaeus by Alex Massey

We can see the Moon's age timeline in the prominent trio of craters Ptolemaeus, Alphonsus and Arzachel. Ptolemaeus (2900 meters deep from rim to floor) is the oldest of the trio, being so filled in by lava it is almost a ghost crater. Alphonsus (3200 meters deep) formed many millions of years later, with the flooding lava nearly totally swamping the central peak. Arzachel (3950 meters deep) formed with very little flooding, with most of the central peak still exposed. Surrounding smaller craters have no flooded floor.

The Moon is\u00a0made of lava

While many people are aware of lava flows being present on the Moon, many again don\u2019t realise that if there was once lava, there must have once been volcanoes! And many of the volcanic features that we see on our terrestrial volcanoes can also be seen on the Moon: shield volcanoes, pyroclastic deposits, collapsed lava tubes, and old lava rivers. All of these are revealed by understanding what the shadows are telling us. These features are invisible when the Sun is high in lunar sky when no shadows can be seen. The shadows reveal their shapes.

Live View Sketch of Moon features Herodotus, Aristarchus, Head of the Cobra, and Vallis Schroteri by astrosketch artist Alex Massey

Possibly the largest shield volcano on the Moon lies right beside one of the brightest features. The brilliant young crater Aristarchus sits right beside the winding, 10km wide Vallis Schroteri. This \u201cvalley\u201d is actually a very ancient and wide dry lava river. The head of this valley has the nickname of \u201cthe Cobra Head\u201d. The Cobra Head is a massive shield volcano from which much of the surround lava fields poured out.

Curiously, there is a much smaller lava river that trickles down the middle of Vallis Schroteri, a much younger and much smaller lava river. Vallis Schroteri peters out into Oceanus Procellarum, the Ocean of Storms.

The most famous shield volcanoes here on Earth are Hawaii\u2019s Mauna Loa and Kilauea volcanoes. Their lava rivers can be found pouring molten red from their massive calderas.

We can see shapes in shadows

Our imagination is wild. Our mind instinctively sees patterns in what would otherwise be visual noise or chaos. This phenomena is called apopheia or patternicity.

In the chaotic and rugged surface of the Moon, shadows play tricks on our human minds. And from the shadows we see animals, trees, faces, even letters of the alphabet, numbers, maps and other symbols. All of these features are also only visible for just a couple of hours as then the shadows change so much that these patterns are no longer visible.

The Lunar X is one such feature, created when the shallow Sun illuminates only the very rim of three craters that are near\u00a0each other. An owl\u2019s face can be seen formed out of two craters, and a little fat owl is formed out of three craters.

The terrifying forces that create craters also results in damage occurring to existing craters. This damage also results in shadows that form creating patterns that are nothing less than remarkable in their resemblance to some very terrestrial features, such as a map of Australia.

Live View Sketches of Moon features Lunar X, Mercator's Owl, Maurolycus (with shadow in the shape of Australia) by astrosketch artist Alex Massey

Summary

Shadows show the shapes of things. In this article we toured some of the Moon's features that are revealed by looking at shadows. In the second article on shadows we'll explore Deep Space Objects.

Editor's Note

Please visit Alexander Massey's incredible blog to see his expanding collection of astrosketches.

Also, Alex is based in Australia - and sees the Moon "upside down" from the way northern hemisphere viewers see it! Have a look at this Arizona State University moon survey map tool for the three craters that Alex drew from his eyepiece. Compare the two views. You can see that the map is biased toward the northern hemisphere\u00a0 - every moon map I have ever seen is rendered from a northern hemisphere orientation.

Galaxy Rise

Fri, 22 Dec 2017 11:46:24 GMT

Physical Astronomy by Daniel Cummings

The Sun rises. The Moon rises. Stars rise. The Galaxy rises - twice. Each day the Earth rotates and sky objects (seem to) rise in the Eastern sky. The Sun, the Moon, the Stars, and the Galaxy rise at various times. The Sun "rises" once-a-day at the start of the day. The Moon "rises" once-a-day at different times of the day and night depending on the moon's orbit around the Earth (its phase). The Stars "rise" once-a-day - all night long, one after another and in groups. The Milky Way Galaxy "rises" twice a day - once on its bright (center) side and then 12 hours later on its dim (outer arm) side. We can orient our bodies to the rising of the Milky Way. And we can experience our daily movement as "plunging through" this flat disk of stars.

The Sun aligned with the Galaxy center

Right now the Sun and the Galaxy center rise at the same time around the Winter Solstice. Once a year they are perfectly lined up in the sky. However, this alignment is temporary! If you can wait about 13,000 years, the Sun will seem to move slowly across the sky. It will move from being aligned with the Winter Solstice point (the Earth's Northern Hemisphere is tilted away from the Sun) to the Summer Solstice point (the Earth's Northern Hemisphere is tilted toward the Sun). Eventually, the Sun and the Galaxy center will rise together at the Summer solstice. The reason this happens is because of a 26,000 year cycle called the precession of the Earth's axis. We are going to learn how to "see" the Galaxy Rise in the winter and the summer The Sun and the Galaxy Center rise together in the year 15,000.

Align your body with the Galaxy by following Cygnus

The Milky Way is a giant physical structure. We are inside the Milky Way. It is quite dim so if you are lucky enough see it in the sky this exercise will be easy to follow. Now, let's say you can't "see" the Milky Way in your sky right now - most likely this is because you live somewhere with a lot of light pollution - sadly, most people can't see the Milky Way anymore. But, you still want to see the Galaxy rise. Here's how you can do that...

Finding Cygnus, flying through the Milky Way

There are several bright stars and notable constellations that help us see the Milky Way even if we can't see it. Cygnus (the swan - a summer constellation) will show you the Milky Way high overhead. Find Cygnus by finding the Summer Triangle asterism. Deneb (the tail of the Swan) is the brightest star in this constellation. Cygnus appears to be flying through the Milky Way heading toward Sagittarius

Finding Sagittarius, Finding the Galaxy Center

To see the center of the galaxy find the constellation Sagittarius. In the northern hemisphere, Sagittarius is visible through the summer months in the southern part of the sky. It has a famous asterism called the Teapot. This Earth Sky article can help you find it. It also contains the curiously named star: Nunki. These will be our main guideposts for the Galaxy: Cygnus (Deneb) and Sagittarius (Nunki).

Rise in the morning with the Galaxy Rise

Once a year the Sun and the center of the Galaxy line up. Right now in our time period in history this happens near the Winter Solstice in December. So, if you want to experience the Galaxy rise, you can experience it in December by watching the Sun rise. The light of the Sun blots out the dim light of the stars and galaxy, but, rest assured, it is there, behind the Sun - rising at the same time. At the Winter Solstice in the northern hemisphere the Sun and the Galaxy center appear to be lined up.

The angle of the Galaxy

Our Earth and Solar System are closely aligned - the tilt of the Earth (as measured from our equator) is only 23.5˚ off angle from the plane of the Solar System. However, the plane of the Galaxy intersects the plane of the solar system at a 60˚ angle. This means that the Galaxy does not easily "fit" into our normal view of sky objects. However, we can orient our bodies to bring them into alignment with the galaxy. This will help us feel and understand the position of the galaxy. To "correct" this angle and make it into a "horizon" you need to lie down. Put your head down on a nice soft pillow with the top of your head facing north and your feet pointing south. Roll onto your side and face east. You have now "corrected" your galactic angle. Imagine the rotation of the Earth toward the "rising" galactic center is carrying you "through" the galaxy plane. As you lie there - if you could stay sleeping like this for 12 hours - the galaxy center will rise past you, then the galaxy's outer arms will rise.

Rise in the evening with the Galaxy Rise - Antares and Vega

Antares (in the constellation Scorpio) and Vega (in Lyra) are two of the brightest stars in the summer sky. They both rise about 1 hour before the center of the galaxy rises. These stars always rise early in the summer evenings and hang in the sky through the night so you can easily find the galactic center - it is just below them (to the left of them if they are high in the sky). Scorpio and Lyra and their bright stars Antares and Vega with the galaxy rise behind them.

Summary

The plane of the Milky Way galaxy is fun to find and easy orient to if you have the right guideposts: Cygnus (Deneb), Sagittarius (Nunki), Scorpio (Antares), and Lyra (Vega). We can watch the Milky Way galaxy center rise in the early summer skies. If we wait long enough, the outer arm of the Milky Way galaxy will rise as well. This double Galaxy Rise repeats every day.

Comments

John Cummings - January 1, 2018 at 5:23 PM

Altair, Deneb and Vega make up the “Navigator’s Triangle.”

starinastar - January 1, 2018 at 5:50 PM

Thanks for the comment John!

Super Moons

Sun, 03 Dec 2017 13:51:24 GMT

Super Moon

The closest approach that the moon will make on its monthly orbit around the Earth coupled with a Full Moon. The December 3rd , 2017 Super Moon is here! Here is an image showing how the arrangement of the Moon's "Perigee" with the Full Moon results in the Super Moon. Schematic showing how the "Super Moon" happens and the change in apparent size of the moon. The Moon appears about 14% larger during a Super Moon event. The Full Moon + Orbit at Perigee = Super Moon.

Stellarium - See the Analemma

Sat, 11 Nov 2017 19:24:54 GMT

See the Analemma

Stellarium can help you see sky patterns and practice Physical Astronomy. Video of the Analemma in Stellarium: By following this article you will be able to see the analemma moving - a figure 8 shaped path that the Sun follows yearly. Above is a composite image that shows the position of the Sun in the morning sky each week. The pictures show every Sun position frozen in the sky each week at the same time of day: early in the morning. The June weeks are at the top left, December weeks at the bottom right and April and September weeks are in the middle at the crossing of the figure 8. The analemma is easier to see when it is animated. In this visualization we will be using the Time Control features of Stellarium. Here is a quick tutorial on time control. Open Stellarium on your computer. (Download it here if you don't have it already).

Set Time Control to Dawn

Set the time to around 7:00am local time. Use time speed control keys J, K, L. Time Controls by Key presses 8 to go to "now", J, K, L to do Time Lapse

Find the Sun

Command + F and type "sun" (with no quotes) into the window. Hit the return key to select Sun.

Lock onto the Sun

Lock the Sun into the viewport using the Space bar. This will keep the Sun in the viewport as we do some time travel. Stellarium screenshot showing the Sun locked in the viewport.

Zoom to show sky and ground

Get to a good zoom level using the scroll function on the mouse or trackpad. A good zoom level is where you can see a little bit of ground and the Sun is in view. Stellarium screenshot - Sun at a good zoom level locked into the viewport.

Time Travel

To see the Analemma we have to do some time travel. We are going to do a Day by day time lapse. Use the Plus (+) or Minus (-) keys to go day by day. Use the Left Bracket or Right Bracket keys to go week by week. Time Controls by Key presses - time jumping: equals, minus, left and right brackets Each time the day or week jump keys are pressed the Sun will seem to move in the sky. Observe the Sun moving in a figure eight shape, tracing out the analemma over the course of a year. The Sun hits the high point at summer solstice (June) and the low point at the winter solstice (December).

Advanced

This image, animation/visualization is correct for the Northern Hemisphere. At the equator the analemma is laying on its side. In the Southern Hemisphere, the Analemma would be upside down - the big loop of the figure 8 on top. You can use the Z key to turn on "Zenith grid" to see the exact degrees of change as the Sun travels on the Analemma path. You can also try out the Equatorial and Azimuthal mount feature in Stellarium. The mount style will change the way the Earth moves on the screen. Use Command - M keyboard shortcut for that.

Analemma References

A really neat article on scienceblogs that talks about the analemma in depth.

Walk to Mintaka

Sat, 04 Nov 2017 14:49:20 GMT

Physical Astronomy by Daniel Cummings

As you walk toward the equator, Mintaka appears to rise higher in the sky. In this post we will learn how to use one bright star of Orion's belt to visualize the Earth's equator.

Mintaka is a Star in Orion's Belt

When you look up at the winter sky in the northern hemisphere, Orion and his famous belt are impossible to miss. The belt is made up of three stars of equal brightness. One of these stars is called Mintaka and it is a guidepost for finding the Earth's equator in space. Yes, the Earth's equator projects out into space. That might seem strange to think of the Earth's equator being in space. If you can imagine the Earth with rings like Saturn, projecting the equator into space would look something like that.

Finding Mintaka

Seen from the Northern Hemisphere, Mintaka is the rightmost star in Orion's Belt. Mintaka is the perfect guidepost for us because Mintaka is located almost directly "on" the Celestial Equator - astronomers call this the "projection of the Earth's equatorial plane into space." In other words, if you are located at the equator, this star appears to rise from due east, be at the highest, overhead point in the sky at midnight - the zenith - and set due west. If you are not at the equator, and you are in the Northern Hemisphere, Mintaka appears in the southern part of the sky. The closer you are to the equator the higher Mintaka goes. Every step you take southward towards the equator makes Mintaka rise higher in the sky. This is because the Earth is shaped like a ball and we are walking on the surface. So, as we walk, our perception of what is directly "up," changes.

Walk to any star

This applies to any star - stars like Mintaka at the celestial equator and stars like Polaris at the northern pole. As you walk "toward" the latitude where the star "sits," the star rises higher and higher until it is overhead at the zenith. For instance, when you are at the North Pole, the North Star is directly overhead.

Summary

As we move to different latitudes on the Earth we are "under" different stars. We walk to Mintaka to imagine the bright stars of Orion's Belt climbing higher and higher in the sky. With every step we take toward the equator, Mintaka rises.

Quiz - When is the best time to see Venus?

Sun, 15 Oct 2017 22:04:24 GMT

See Venus

What time of night is the best time to see the planet Venus? Is it sunset, midnight, or sunrise? None of these? All of the above?

Think about it for a few minutes before reading on.

The answer is that the best time to see Venus is either at sunset or at sunrise. Venus is never visible from the Earth at midnight.

This is because Venus orbits closer to the Sun than the Earth does. To see Venus, we always have to look somewhat towards the Sun.

Midnight is the time of night when the Earth is facing away from the Sun. When we Earthlings look up at the sky at midnight, we are looking directly away from the Sun.

We can still see the outer planets at midnight because they are further away from the Sun. But at night, the Earth itself blocks our view of Venus just as it blocks our view of the Sun.

Comments

Tulia W. - May 16, 2018 at 9:53 AM

I never realized this fact about Venus. Thank you for sharing. Love the website, BTW.

Tilt Head to Tilt Earth - Seasons are caused by a tilted Earth

Tue, 26 Sep 2017 14:12:00 GMT

Physical Astronomy by Daniel Cummings

Seasons are caused by a tilted Earth

Use this technique to understand how seasons happen on the Earth. The Earth is tilted. When the northern part (your forehead and eyes) tilts away from the Sun the season is winter. When the northern part tilts toward the Sun the season is summer. The Earth is tilted as it spins daily - it is not straight up and down like a top, but more like the Leaning Tower of Pisa (if the tower could spin!). As it goes through its yearly orbit, the Sun hits the northern and then the southern parts of the Earth.

Tilt your head to tilt the Earth

In this model, when the northern part (your forehead and eyes) tilts away from the Sun the season is winter. When the northern part tilts toward the Sun the season is summer. Did you like this season model? Any questions? Type in the comments to send me a message.

The Moon is Upside Down

Fri, 15 Sep 2017 13:58:27 GMT

The Moon is Upside Down

The moon as seen from the Southern Hemisphere. source: Wikipedia (rotated). When you are in the southern hemisphere, the moon looks upside down. When I came back to the US from living in Australia for 4 years, I published a poster with a picture of the moon on in and I placed it “upside down” - someone pointed it out and I looked at the moon and said “the moon is upside down.” This was true - in the Northern Hemisphere - but to people living in the Southern Hemisphere the moon appears "upside down." I was shocked, but the claim was true - in the Northern Hemisphere! But to Australians and other people living in places in the Southern Hemisphere the moon appears "upside down."

Train Your Brain - The Sky Below Us

Wed, 26 Jul 2017 13:51:38 GMT

The Sky Below Us

Physical Astronomy by Daniel Cummings

In this exercise called "The Sky Below Us" you will learn to see the Earth as a giant ball and understand that the Earth is floating in space. This will allow you to see the sky below us. Go outside on a clear day. Look down. What do you see? Your feet. The floor. The ground. Look up. What do you see? Trees. Buildings. The blue sky. Look down again, but this time... imagine that there is a hole through to the other side of the Earth. Imagine that you can see clear through to the other side. Imagine that you can see the sky below at the "bottom" of that hole. If it is daytime where you are then the other side of the Earth is in night... you should even be able to see some stars in the sky below. A hole in the ground to the other side of the Earth.

Antipodes (an-TIP-ode-ees)- the other side of Earth

Now, imagine somebody thousands of miles away at the "bottom" of that hole on the exact opposite side of the Earth - at the antipodes. They are standing up straight just like you are. When they look up they see their own sky and when they look down, they see a hole in the ground and they see your sky. Both of you have sky "below" you. We tend to see up and down as fixed properties of being on the Earth, but as you can tell from this simple exercise, they are not fixed properties - up and down are relative to the nearest gravitational object.

Earth as a ball

Now, close the hole and look down at your feet again. Imagine that when you look down at your feet instead of standing on flat ground you are standing on a soccer ball that is the shape of the Earth. Imagine that you can see the edge of the Earth curling under you - blue oceans, white clouds, green and brown landforms, the icy poles. Imagine what it would look like if the horizon gathered in under your feet and you are standing on top that big ball. Maybe the ball changes size until it is as big as a house or an elephant. Maybe the ball is as small as a tennis ball. Beyond the ball and below the ball now is all "sky" (let's imagine the sky stays blue). Behind the blue sky is a field of stars in every direction. If the Sun were to go dark for a time, the sky would go black and the stars would shine intensely all around.

Summary

This exercise should help you envision the sky below us. At the end of this Train your Brain exercise you should be able to imagine the Earth as a giant ball floating in space.

Comments

Pingback: […] are not above the Arctic circle… if you could look right at the Sun at midnight – by looking through the Earth – which cardinal direction would you be facing? East, West, North, or […]

Train Your Brain - The Speed of Day

Sun, 16 Jul 2017 22:29:04 GMT

Physical Astronomy By Daniel Cummings

The Speed of Day

The "speed of day" is the speed of Earth's rotation: 1600 kilometers per hour (kph) which is about 1000 mph. 1600 kph is fast. Most people have never experienced anything moving at this speed. Commercial jet airplanes fly at 1000 kph (600 mph). However, it's hard to understand that speed because we don't ever see them flying at ground level. The speed of sound is 1200 kph - the Earth's rotation (at the equator) is carrying us 400 kph faster than the speed of sound. That is incredibly fast! By using our imagination and "seeing" the speed of day we can understand just how fast we are moving. And by understanding how fast we are moving, and feeling just how long a day is - even at such a breathtaking speed - we can really feel the size of the Earth.

Stop Time

Let's start by stopping time. Pretend that everything is stopped. The Earth has stopped rotating and orbiting. It might seem strange to stop time to see something move, but it helps us to get our visualization right. Pretend that you stop time at noon and you are standing outside facing southward. The Sun is now stopped in the sky at exactly noon at the highest point in the sky.

The Noon Curtain

So far we haven't imagined anything too weird. But, we are about to add something nobody has ever seen before. Imagine that there is a very thin (1 cm thick) north-south, glassy, shimmering curtain of light (as thin as a veil) that ripples down from the Sun in the sky. The thin curtain or veil of rippling light is oriented directly north and south. Because it is noon, this "noon curtain" drops from the Sun directly above you. The curtain appears to originate high above the atmosphere and drops down through the sky right down onto your head. It stretches to the north and south as far as you can see. You can step to the left (east) and the curtain is to your right. You can step to the right (west) and the curtain is to your left. You can see it reaching from the Sun down to the ground like a gigantic shining, glowing curtain of light. This "noon curtain" helps us visualize the line of noon in the sky. Every point on the Earth passes through this curtain every day at noon. And remember, what we call noon is the time of day when the part of Earth we are on passes "through" this curtain. Time is still stopped right now so the noon curtain is not moving.

Start Time

Let's restart time, slowly, to see what happens to the curtain of light. Still facing southward you see the giant curtain begin to slowly "move" toward the west (the right). As you know, the curtain is not actually moving; it is us moving. As time returns to normal the curtain begins to "move" faster towards the west. Really, as the Earth rotates, you are carried further and further away from the noon curtain. The curtain is "moving" because of the newly resumed movement of the Earth. You see the curtain seem to travel away westward but it is actually us traveling away eastward. Eventually, the sun will "set" - actually the Earth carries us until the Earth itself begins to block our view of the Sun - and the sun and the "noon curtain" will disappear. All we have to do is to speed up time until just before noon the next day.

Slow Time

This time, to experience the noon curtain, instead of stopping time we can just slow it down a lot. Let's slow down time by 300 times so that as the noon curtain approaches us from the east (actually we are carried through it), the curtain floats in at a slow walking pace (about 1.5 meters per second). Imagine the towering curtain of light floating towards you from the east. It is moving as slow as a person walks. It crosses past you and it continues westward. During this noon curtain passage time is slowed so the Earth's rotation is also slowed by 300 times. This is a speed that seems like it might correspond to the "speed of day" - the day goes by so slowly and the movement of the Earth is barely perceptible. However, the Earth rotates 300x faster than walking speed.

Normal Time

For the last visualization let's imagine passing through the noon curtain at full speed. What would that look like? 1 kilometer every two seconds. The noon curtain spreads across the sky and we speed under it.

The Size of the Earth

The distance we move to meet and go through the noon curtain is immense. Every day, 24 hours a day, the Earth rotates, carrying us on its surface under the noon curtain. As you get good at visualizing this transit of the noon curtain, you can begin to feel just how big the Earth is. Imagine the curtain "moving" constantly at this high speed for the entire day. This is the speed of the Earth's rotation. We are carried along under the day at the speed of Day.

Summary

460 meters per second. Every day. The speed of day.

Arms around the ecliptic

Tue, 27 Jun 2017 12:58:05 GMT

Learn to see the ecliptic

Physical Astronomy by Daniel Cummings

The sun follows the same path through the sky every day. Sun up. Noon. Sun down. The sun starts the day in the east in the morning, rises high in the sky at noon, and settles down again in the west for a nap at night.

See the ecliptic

Here is an exercise to discover that path - the ecliptic. At noon, face south, put your hands together, point both hands at the sun, bend your arms slightly at the elbows. Keep your elbows high, and pull your hands toward your face until they are about 6" away. From your left elbow through your hands to your right elbow, your arms are tracing the path that the sun follows each day... the ecliptic. And it's not just the Sun following the path of the ecliptic. All major solar system objects (the sun, the moon, and the planets and sometimes comets) seem to follow this path through the sky. So, now that you can "see" the ecliptic as a line across the sky we can talk about what it really is. It's not exactly a path that sky objects follow... as you know, planets follow their own paths around the sun, their orbits. It's a combination of their own path and our movements here on earth.

Earth moves, not the Sun

Also, you might be asking why, if the sun is the center of the solar system, does it "move" at all? And also, why, if the moon is orbiting the earth, does it too follow the path of the ecliptic? All good questions. And there is a simple answer: the Earth rotates each day and makes it seem as if the sky objects are moving. This is worth repeating. It only appears that objects are moving. It is the earth moving and we are carried along on it. So, objects in the distance only seem to travel across the sky each day. Since the Earth rotation is stable and repeats, when we look up at the sky, the sky objects seem to move.

Solar System Disk

There is one more thing that keeps all the solar system bodies "on" the ecliptic path. It has to do with the solar system disk. All solar system orbits are aligned with each other in their orbits - except for Pluto and the other planetoids like Eris and Ceres. The orbits look like a set of neatly nested concentric rings that lay flat like a plate. The planets all orbit the sun in the same plane. Image not to scale. It is the combination of this flat plane of orbits and the daily movements of the earth that give rise to the ecliptic. The earth is orbiting yearly in this same flat plane orbit so our observing position changes over the year. However, the ecliptic stays the same.

Summary

With this simple physical motion you can make the ecliptic visible any day. Put your arms around the ecliptic and discover one of the great physical astronomy sky patterns!

Quiz - Do you Moon Phase?

Thu, 15 Jun 2017 07:26:40 GMT

Moon Phase Quiz

Examine this image of Moon phases made from emojis. Reading left to right, which row shows the correct sequence of Moon phases? Did you guess yet? The answer is below. Row 3 is the correct answer. Row 1 is almost correct except for one Moon phase. A Strange but True FACT ... the Moon - when viewed from the Southern Hemisphere - goes through the same phases but upside down! So, Row 3 is correct but only if you flip the quiz upside down and then read the sequence right to left.

Moon phase emojis

Copy this list of moon emojis and send to your friends. 🌕 🌖 🌗 🌘 🌑 🌒 🌓 🌔 🌕

Train your Brain - See the shape of the solar system

Mon, 29 May 2017 11:38:57 GMT

Physical Astronomy by Daniel Cummings.

See the solar system from Earth

Most people, when they look up at the night sky can easily see stars and identify some familiar groups of stars (asterisms and constellations). Some people can even find and name some planets - Venus, Jupiter, and Mars are all bright and easy to see.

But, there are many invisible wonders in the sky - and some of them can be seen without a telescope. In fact they are so big that a telescope is not the right tool to use; we have to use something even more powerful... imagination!

Using visualization and imagination, I am going to show you how to find and "see" a very large structure in our sky: the solar system disk itself. Through this exercise you will learn to identify planets and use them to trace out and see the solar system disk in the sky. You will learn to imagine the orbit trails of Venus and Earth and the Moon as if they were visible. You will follow Jupiter's 12 year journey across the constellations. And when planets are "lined up next to each other" you will be able to understand and visualize the deep space distances between them.

The solar system is a disk

The solar system is a disk. We can learn to see it, luminous, ancient, traveling. We are a part of that disk, always moving inside it. From our point of view on Earth, the disk of the solar system is always visible as a line in the sky - if you know how to see it.

The planets all orbit the sun in the same plane. Image not to scale.

Venus at midnight

The bright planet Venus will be our first guidepost. Venus is easy to find because it is the brightest object in the sky after the Sun and the Moon. It's the first object that becomes visible as we move into night.

Let's start with a question about Venus: Yes or No... can we see Venus at midnight? Think about it for a minute. I'll give you the answer a few sentences from here. When do you normally see Venus in the sky? At night, right? But, for how long into the night does it remain visible? Does it stay up in the night sky until midnight?

The answer is no, we can't see Venus at midnight. The reason is because Venus is too close to the Sun. It will never appear in the middle of the night sky. At midnight, the part of the Earth that we are on has fully turned away from the Sun, we are looking into space in the opposite direction from the Sun, and we experience night. Night is when the Earth blocks our view of the Sun and it will block our view of Venus too. Venus orbits closer to the sun than we do so it always hangs close by the sun. At night when the sun is hidden, Venus is hidden too. (The Sun's closest planet Mercury is hidden too.)

Here is a drawing showing the orbits of Venus and Mercury just after sunset. It is not to scale. However, it shows how the two orbits are fully visible to people on earth. There are no lines in the real sky showing the orbits, but you can easily imagine them after seeing an image like this.

Orbits of Venus and Mercury as seen from Earth at sunset. Design credit to NASA illustrator: https://history.nasa.gov/SP-424/ch1.htm

In fact, if you want to see a version of this image showing the way the real planets are arranged, you can grab a copy of Stellarium. You can set Stellarium to show you the planet orbit trails.

See the Earth's orbit

You can also learn to see the orbital path followed by earth. This is another way to begin to see the solar system in the sky.

Let's start with another question and answer. Imagine if you could look up in the sky and see the orbit trail of the Earth. As if the Earth's path through space were marked by sparkly, glowing dust! Where would you look? Would the orbit trail appear to be near the Sun and appear during the day? Or would it be visible at night? If night, what time of night?

I am going to teach you a trick that uses the moon to help you "see" the Earth's orbit. The trick is to find the moon at its quarter (so-called half moon) phases. The moon in these 2 phases shows you where the earth's orbital path would be if it were visible.

There are two points in every moon cycle where the moon's orbit crosses the orbit of the Earth: the 1st and 3rd quarter moons. At sunset at the 1st quarter moon and at sunrise at the 3rd quarter moon, the moon, the sun, and you are oriented in a way that makes it easy to "see" the Earth's orbit. When you look up at the moon you are seeing where the earth was (1st quarter) and where the Earth will be (3rd quarter).

It's a really incredible, dizzying feeling to look up at the moon and realize that it shows you where the Earth's orbit is... especially during the 3rd quarter moon where the moon is like the tip of an arrow flying through space ahead of Earth on its orbit.

The Horns of the Moon

The moon gives us another guidepost in this exercise - it can help us to see the solar system. As it moves through the sky and goes through phases, it always "points" towards the Sun.

Horns of the waxing moon point along the moon's orbit

First, another question: You know that the moon orbits the Earth, but which direction and by how much does the moon move in the sky each day? Think about it for a few seconds now... does the moon move north to south or east to west or west to east or south to north or some combination? Does it change direction or always move in the same direction?

The answer is that the moon moves toward the dawn. Its orbit around Earth makes it appear to move eastward through the sky.

Also, the Moon changes shape as it orbits the Earth. At the crescent phase the Moon has "horns" and these horns are like pointers that help you visualize the plane of the moon's orbit and also the solar system. The moon's orbit is roughly aligned with the solar system disk and the ecliptic (the path the Sun appears to travel through the sky each day). So, if you can see the direction and orbit of the Moon, then you can come pretty close to the ecliptic and from there see the entire plane of the solar system.

Jupiter's 12 year trip around the Sun

Jupiter takes 12 years to travel around the Sun. From the Earth, over the course of 12 years, Jupiter appears to move slowly through all of the sky. Year by year it moves from one constellation to the next - always eastward toward the dawn. Right now, in early 2017 Jupiter is "in" the constellation Virgo. But, next year this time (March 2018) it will have moved "into" the constellation "Libra." It will eventually cross all of the Zodiacal constellations, Scorpio, Sagittarius, Capricorn, etc... in a stately 12 year cycle.

When you look at bright Jupiter you are seeing an object that is between 588 million to 968 million kilometers away. Light itself takes between 34-54 minutes to travel from Jupiter to Earth.

Sometimes the planets are "lined up" in the sky, with Venus seemingly "next to" Jupiter or Mars. This is the perfect time to look up at the planets and contemplate the fact that they only appear to be lined up because one is in front of the other from our point of view - it's like the more distant planet is "photobombing" the other's picture by appearing in the distant background.

Summary - See the Solar System

These visualization techniques can help you see the solar system. You can use these tricks day or night. The Sun is the center of the solar system so when you look at the sun you are looking at the hub of a vast and knowable structure. I use these imagination tricks to stretch my vision of what is "up there" and to help me see the great geometries of space. Please share your experiences and comments below.

Comments

Pingback: […] My goal with this new way of teaching astronomy is to bring curious young minds fun, high-quality, experiential, developmentally tuned lessons for getting involved in the process of scientific […]

Sarah W. - April 19, 2018 at 10:01 AM

This is really interesting! I like how you provided a few different ways to see the shape of the solar system.

Night is...

Sat, 13 May 2017 23:07:22 GMT

"'Night' is not what time it is... it is where you are." - Daniel Cummings

Stellarium - Control Time

Wed, 26 Apr 2017 07:32:25 GMT

Stellarium lets you control time.

Stellarium for Physical Astronomy

Learning to do Physical Astronomy? Stellarium is the perfect tool for you. It helps you learn to see patterns in the sky. In this article you will learn how to use the Time Control features of Stellarium. You can use the excellent time controllers to move the clock backward and forward. You can speed up time into a time-lapse, slow it down, or move it backward. You can pause time with Stellarium (hint: press the k key to start and stop time). You can jump to any moment in time - even back to the time of the Egyptian Pharaohs. You can jump by an hour, day, or week. You can use it to plan viewings or to check what you saw in the sky.

Time-lapse to the future or the past

Time controllers give you control over time. You can stop time, speed it up, and go in reverse. And if you find you are stuck somewhere in the past or the future you can easily get home! Speed up time just a little bit (hit the L key a few times or click the double-right arrows) and you will immediately see the stars begin to move across the sky. Notice which direction they are moving? They "Rise" in the East and "Set" in the West - just like the Sun - in fact, every star is like a setting sun. The control bar Stellarium - time controls are triangle shapes on the right side Time Controls by Key presses 8 to go to "now", J, K, L to do Time Lapse You can click the button on screen or use a key press.

Set time to "now" - press the 8 key or click the "hourglass" button
Increase the speed of time - press the L key or click the "two triangles pointing right" button
Reverse the speed of time - press the J key or click the "two triangles pointing left" button
Stop time, Pause time - click the K key or press the "play" triangle (it will turn into a pause button)

Time travel by Hour or Day or Week

Timelapse is cool - but sometimes you want to jump a specific amount of time forward or backward. For instance, you might ask yourself "what will the moon look like and where will it be at this time tomorrow?" The plus and minus keys can help you see that. Time Controls by Key presses - time jumping: equals, minus, left and right brackets

Move time by 1 hour - forward (press Command/Ctrl and equals =) or backward (press Command/Ctrl and minus -)
Move time by 1 day - forward (press equals =) or backward (press minus -)
Move time by 1 week - forward (press right bracket ] ) or backward (press left bracket [ )

Lock on object to keep it in view

Often you will want to look at a particular patch of sky and watch it go by, but other times you will want to "lock" onto an object and follow it, keeping it in the view. The Moon is a great object to lock to and track. The Sun is also a good target to lock onto. C-ombine locking with time-lapse and you will really begin to unlock the motions of the sky. Click an object to select, space bar locks on that object - the view will follow it

Space bar is a control for locking your view on a certain object. Just click the object and hit the space bar. All time controls will still work, but now the view will track that object.

Zoom it!

Stellarium gives you a super zoom ability and can make your computer as powerful as the Hubble Space telescope. Try locking onto the moon and zooming in. Jupiter is another beautiful sight fully zoomed in! Once you zoom in all the way, you can see Jupiter's moons. Combine these three tools for a treat: lock on Jupiter, zoom in all the way, and start a time-lapse and you've just recreated Galileo's world-shattering scientific observations. Command / Ctrl up or down arrow to zoom in and out

Zoom in and out of the viewport - Command / Ctrl up or down arrow or "scroll" with the mouse wheel or trackpad

Advanced - Time travel by Sidereal day

Earth's orbit combined with daily rotation means that a day isn't really a day. There are actually two types of day on earth: a normal day where we see the sun appear in the same part of the sky 24 hours later and the sidereal (pronounced "sye - DEER - ree - all") Use the option key to jump by sidereal time instead of "normal" time.

Advanced - Azimuthal v equatorial mount

This is an advanced technique to explore as you get more comfortable with the other tools. The choices of the type of "mount" are equatorial (what we think of as "normal" view) or "azimuthal" (the way some telescopes are angled). The azimuthal mount can sometimes highlight certain types of sky motions better than the equatorial mount. Command / Crtl M to change telecsope mount, Command / Ctrl up/down arrow to zoom in and out

Mount switch - Command/Ctrl + M changes the type of angle you are at when viewing the sky.

Stellarium is a deep and complex software tool that will improve your Physical Astronomy observations. I've shown you how to control time, lock on an object, zoom, and see the sky at different angles. These are just a few of the controls available. I trust you will have fun. If you have any questions, just contact me and I'll be happy to chat.

Comments

Pingback: […] it is animated. In this visualization we will be using the Time Control features of Stellarium. Here is a quick tutorial on time control. Open Stellarium on your computer. (Download it here if you don’t have it […]

Pingback: […] you don’t have Stellarium, you can download a copy here. And I have a few tutorials that can help you get started with this amazing piece of […]

Desmond Kelly - May 31, 2018 at 8:52 AM

Thank you for sharing this tutorial on Stellarium! It was very helpful. Des.

starinastar - June 13, 2018 at 2:35 PM

Thanks Des. Much appreciated.

Stars like ours - 9 bright "Life Stars"

Wed, 12 Apr 2017 20:47:27 GMT

Life Stars - Visible Exoplanets

Physical Astronomy by Daniel Cummings

A "Life Star" is a visible star that could host life. This is a name I came up with in February 2017 (around the time of the TRAPPIST announcement) to describe _visible stars with confirmed planets orbiting in the habitable zone. "_Life Star" is easier to say and explain. I hope it catches on!

So many exoplanets

Since the first exoplanet was discovered in 1992, Astronomers have found thousands of stars in our galaxy that have planets - more than 3200. Most of them are not visible to the naked eye. Also, most of those exoplanets are not the most exciting kind. The most exciting kind of exoplanets are planets orbiting in the "habitable zone" of a star. For instance, the star featured in the recent announcement of 7 potentially Earth-like planets orbiting the nearby TRAPPIST system is not visible to the naked eye. So, while it is exciting to know that this star is "out there somewhere," it is not possible to experience it in any physical way. You can't see it. You need to see something so you can feel connected to it. Luckily, there are a few bright and visible stars with exoplanets that also orbit in the habitable zone. These are what I call Life Stars. These are stars that have confirmed planets that could potentially have some form of Life on them. And the coolest thing is that you can look at these stars without any special equipment. When you have finished this tour you will see these stars with a new perspective. And now, you can point to them and say "These points of light could potentially host life." That fact makes them different from the rest of the stars. It's easy to imagine that there are alien creatures or even alien civilizations in those star systems. Some of these exoplanets have even been given official names.

A Trip through the brightest Life Stars

The brightest known Life Star is Pollux. This is also one of the brightest stars in the sky so it makes a good starting point for our trip. In the image below you can see the 5 brightest Life Stars circled in red. The bigger the red circle, the brighter the star. The 5 brightest Life Stars - Pollux, Kochab, Algeiba, Errai, 7 CanisMajor Note: All images in this listing are generated using Stellarium and show what the sky looks like approximately 8pm on Earth Day April 22nd, 2017 in the Northern Hemisphere.

1. Life Star: Pollux

Pollux is part of the constellation Gemini (The Twins) and is visible at night throughout the northern hemisphere Winter and Spring. It is easy to find because it is part of the Winter Hexagon and it stays right next to its equally bright twin, Castor. Pollux's exoplanet is named "Thestias" after Pollux and Castor's grandfather.

2. Life Star: Kochab

Kochab is part of the Little Dipper. It is the brighter one of the "guard stars" that make up the Little Dipper. Kochab and its partner Pherkad are the pouring "lip" of the Little Dipper. They are called guard stars because they circle the North Star every day like a pair of watchful guards. Visible year round in the northern hemisphere it is a brilliant example of a Life Star because you can see it anytime!

3. Life Star: Algeiba

Algeiba is the star that is the neck (or mane) of the constellation Leo - the Lion - just to the north of the bright star Regulus. It forms the middle part of the "sickle" asterism that sits in the constellation Leo. This star is visible through the Spring and Summer.

4. Life Star: Errai

Errai looks like it might be the pointy tip of King Cepheus' hat, but it is actually the king's knee. It is a circumpolar star that is visible year-round. This star is easier to see in the Summer and Fall seasons. "Tadmor" is the name of Errai's exoplanet - named for the Syrian city of Palmyra. Now we start to get into the stars that do not have historical names, but they are still bright enough to see.

5. Life Star - 7 Canis Major (close to Sirius)

Sirius is the brightest star in the sky and 7 Canis Major is in the same constellation (Canis Major - the big dog). This Life Star is easy to find. Just find Sirius and look a little bit south/down toward the horizon. It's between and to the left of Sirius and the bright star Mirzam that marks the foot of the big dog. I think of this star as the heart of Orion's Big Dog.

6. Life Star: 50 Andromeda (close to Almaak)

Andromeda is a Fall and Winter constellation. This star (50 Andromeda) is close to the bright star Almaak. This star is still visible under good conditions, but a magnitude 4 star (meaning, not very bright) can get pretty hidden in the suburban sky.

7. Life Star: 11 Corona Borealis (near Alphekka)

The constellation Corona Borealis is a curve of stars next to Boötes and the bright star Arcturus. Alphekka is the brightest of the group and just nearby is 11 Corona Borealis.

8. Life Star: 42 Draco (aka "Fafnir" - near Altais)

42 Draco (named Fafnir after a Norse myth) is between the fantastically named stars Altais and Grumium. Draco is the "dragon" that circles the north star every day. The exoplanet that orbits Fafnir is named "Orbitar."

9. Life Star: 47 Ursa Major (aka "Chalawan" - in the Big Bear, Big Dipper)

47 Ursa Major (named "Chalawan" after a mythological crocodile from Thailand) is quite dim. However, on a clear night with dark skies it is possible to find. It is a magnitude 5 (not very bright at all) star near the Big Dipper about the same distance in the opposite direction from the North Star. Magnitude 5 stars are pretty dim, so this star would be a challenge to find in a suburban backyard - unless you have a pair of binoculars! The 2 exoplanets that orbit Chalawan are named after the twin sisters in the Thai myth "Taphao Thong" and "Tahpao Kaew." Those are the 9 visible Life Stars. Next time you are out under the Northern Hemisphere skies you can find at least a few of them under almost any light conditions. When you look up you can try to imagine life "out there."

Bonus - "Story mnemonic"

If you want to remember a sequence of things (like which stars are Life Stars) you can use a storytelling technique to help remember. We are really good at remembering stories. There is an easy-to-remember story mnemonic for the first 5 Life Stars. If you want to be able to point up at the sky and find these stars, the first 5 can be woven into a story mnemonic to help you remember. Pollux the twin goes looking for a king with a dog. He meets Kochab the guard (the guard star) who has a Lion on a leash (Algeiba the neck of the Lion) helping him protect the King (Errai the knee of the King that looks like it might be the tip of a pointy hat). Pollux eventually meets the Big Dog (7 CMa the heart of Orion's Big Dog). The dimmer Life Stars can be easily woven into the story, as they include Princess Andromeda, A Dragon, A Crown and a Bear. I urge you to try to find these stars as well. Maybe one day soon we'll be able to see what their exoplanets hold! That's the end of our tour! Clear skies everyone.

Summary

Our emphasis is on the visible stars that might harbor earth-like planets. We learned how to find them in the sky. We also learned to weave a path through them using a mnemonic. References: Open Exoplanet Catalog - confirmed, habitable zone planets only Pollux Kochab Algeiba Errai 7 Canis Major

Comments

Jim - January 15, 2018 at 7:04 PM

Very cool! I never thought of stars as having life before. Thank you for sharing this.

starinastar - January 29, 2018 at 3:33 PM

Thanks Jim! The best way to really get this idea is to go outside and find the stars in this guide. Hope this helps!

The Moon teaches you to see Earth's Orbit

Sun, 26 Mar 2017 20:23:00 GMT

See the Earth's Orbit in the Moon

Physical AstronoMy by Daniel Cummings

You can use the moon to "see" the Earth's orbit in the sky and the space beyond. Most people think the full moon is the best moon phase. We get to see the whole glorious sphere lit up full on one side. The full light of the sun brightens the surface of the moon so much that the sunlight reflected off moon makes shadows at night. Other people like the New moon. Maybe it's because it symbolizes new beginnings, or because the moon is hidden in the glare of the sun like it's not even there. My favorites are the two half moons - the first quarter and the last quarter. I like these phases because they show us something beyond the moon. And with a little bit of imagination they allow us to see into the depths of space. The half moons are like helpful guideposts that show you the orbit of the earth. Here's how it works: You have to start with these facts: Fact 1) the earth orbits the sun. Fact 2) if you look up at the sky you are actually looking into space. This is easier to imagine at night when the stars are bright enough to reveal the depth of the sky. During the day we have blue. Fact 3) Every 29.5 days (approximately) the moon orbits the earth. During its orbit, the moon crosses the Earth's orbital path twice! So when you see the moon hanging up there my hope is that you can understand that the moon is up in space being tugged along by the earth. I like to imagine that the moon is crossing a stream of sparkly, dust particles like a trail in space tracing out the earth's orbit.

The Moon follows the Earth

The first quarter moon is ideal for viewing this tugging along. The moon is trailing us in orbit. So, when you look up at the moon in this phase, you are looking at where the earth just was in space! The moon follows the earth.

The Earth follows the Moon

In the last quarter phase of the moon, the Earth follows the moon along the earth's orbital path. It's like the earth chases the moon during this phase. So, when you look up at the moon in this phase, you are looking at the direction the Earth is heading.

The best time to observe

The best time to observe these two phases is at sunset (1st quarter) and at sunrise (last quarter). When you look at the moon in these phases at these times you will be able to see the moon directly "overhead."

Follow-ons

If you could actually see the earth's orbit in the sky, it would mark day and night. It would look like a tall rocket ship cloud trail after launch always directly overhead at sunset and dawn. A family views the visible orbit path of the earth.

Take it out into the world

The next time you catch a glimpse of the half moon hanging in the morning or evening sky, try to imagine the moon leading or following us here on earth as we orbit the sun together. Questions? Comments? Type to me below!

Comments

Pingback: […] trick is to find the moon at its quarter (so-called half moon) phases. The moon in these 2 phases shows you where the earth’s orbital path would be if it were […]

Train your Brain - Day and Night

Sun, 12 Mar 2017 21:26:05 GMT

Train Your Brain - a series of physical astronomy exercises by Daniel Cummings.

Practice the fundamental skills of observation. Learn to see the giant geometries of space. This training exercise will change your experience of night and day.

Experience Night

We think of night as something that comes over us like a blanket as the sky gets dark and the stars come out. It seems like the sun goes hiding "underground" - and in a sense it is. But, it is just hidden "behind" ground as the earth turns. Night is when the earth turns away from the sun. The earth itself blocks the light of the sun. We move into the earth's shadow. To really "Experience Night" and see night for what it is - it's good to begin at sunset. Watch the sun at sunset and feel yourself being carried backwards away from it. Instead of the sun moving, imagine the earth is moving and carrying you backwards at about 1600 kilometers per hour (1000 miles per hour). Each minute you are moving 26 kilometers (17 miles) "away" from the sun. Each second you are carried about 500 meters (5 football fields) backwards. As you move the earth curves into the horizon and blocks the sun's light. This is night - you move into the shadow of the earth. The sun does not move... you move.

Experience Day

Day is when the earth carries us so that we face the sun. We are carried under the sun. We face its full brightness. The earth moves and we move with it. The sun appears to hang high in the sky and travel from east to west. Day happens as we are moved along under the sun. If you can get up early in the morning and see the sunrise, this is the best time to feel the motion of the earth that "makes" day. Watch the sun as it climbs out from behind the earth horizon. The earth is moving, carrying you toward the face of the sun. The sun does not move... it is the earth moving.

Experience Day and Night

In sun, then in shadow. This is day and night. We move under the sun each day and are carried into the earth's shadow each night.

We are Star Sand

Sun, 26 Feb 2017 11:25:58 GMT

Star Sand

Just how tiny ARE we? The answer of course depends on the question: "Compared to what?"

Compared to the size of the universe we are very, very tiny.

Take a quick trip with me and you will begin to understand.

Imagine our Sun is the size of a grain of sand.

Now line up 10 grains of sand. That's about 1 centimeter - the width of the tip of the pinky on your right hand.

Make it a line of 1000 sand grains and you've got 1 meter of sand grains - imagine that these sand grains are 1000 stars - about the number you can see on a very clear night in the suburbs from your back yard.

Now, imagine making that line of grains of sand/stars into a 1x1 meter square "mat" of stars. That is 1000x1000 stars = 1,000,000 (1 million) stars! If you counted these sand grains at a rate of one per second you would be counting for 11 days straight.

Let's go from 1 million stars to 1 billion stars. Make the "mat" of sand a cube that is 1000 grains high and you now have 1 billion stars of sand. 1 billion stars - a massive pile of sand! Each one of them stars, just like ours. To give you an idea how much bigger a billion is than a million... If you counted these grains at one per second you would be counting for 31 years without a rest!

Now, picture a tennis court. And take those 1 meter cubes of sand and cover half of the court with them. Half the court piled 1 meter high with grains of sand. That's about 100 billion grains of sand. Pile it 10 meters (30 feet) high and you've got 1 trillion grains of sand.

In the Milky Way Galaxy (our galaxy), there are between 100 billion and 1 trillion stars (grains of sand).

The Sun is ONE OF THOSE stars (grains of sand)! One.

It's an astonishing idea. Just imagine.

OK, let's amp it up. If you don't feel tiny yet, get ready!

Repeat this process now, but this time imagine a single galaxy is the grain of sand.

Start with 1 grain, then 1000 (1 thousand, the line), then 1,000,000 (1 million, the mat) then 1,000,000,000 (1 billion, the cube) then 100,000,000,000 (1 hundred billion, the half tennis court) then 1,000,000,000,000 (1 trillion, the half tennis court piled with 10 meters of sand).

Wow.

Now, please take a breath before you read the next paragraph.

Scientists estimate that there are about 100 billion to 1 trillion galaxies in the known universe, each containing a similar number of stars to the Milky Way.

Gulp. We are tiny.

Stars in Your Eyes

Sun, 12 Feb 2017 10:00:55 GMT

The light of a star...

...no matter how long it has been traveling through space, ends its journey in your eye. The light hits your retina and is transformed into thought. As long as you let that star light stream into your view, the star itself lands in you and settles its motion. When I was 17 years old I went on a weekend retreat run by the Christian Brothers near Melbourne, Australia. It was a weekend of spiritual teaching, introspection and reflection. Saturday night, one of the other boys at the retreat surprised me. As we stood outside under the stars, he spoke in that matter-of-fact way typical of Australians. Without looking at me, he nodded his head upward - indicating the sky above full with Southern Constellations. He said "The light of the stars we are looking at just finished a journey. Each particle of light we are looking at, was once a part of a star. It's been traveling through space for years. And now, it's gone, and it has become a part of us." Wait, what? I knew that light traveled and that it had a speed. I knew about constellations and moon phases and other astronomy concepts, but I had never before considered star light as a "thing" that could end. That was a radical new concept and gave me a new way of seeing. With that different way of describing and experiencing light speed, I had become more deeply connected to the cosmos. In just a few words - a koan - I had been "enlightened." I knew about the scientific concept of light speed but to me, it seemed now, the stars were in motion. They were dynamic and alive, like a giant being with multiple disparate parts. And - astonishingly - one of those parts was now in me; in my eye. With just a few words the time scale of light traveling through interstellar space suddenly became clear. It was articulated into a precisely human-scaled experience; a human could become part of a star just by waiting and being in the right place at the right time. That night, the light became a part of me. Every night now when I look up at the sky and the light of a distant star lodges in my eye - it continues to teach me how to connect to the stars.

Groundhog Day Shadow Tracker

Wed, 01 Feb 2017 23:35:43 GMT

Physical Astronomy Tool by Daniel Cummings

It's Groundhog Day!

What better way to celebrate Groundhog Day than to Build your own Groundhog Day Shadow Tracker

UPDATE: We now sell an astronomy gift called the Sun Tracker that teaches you the same Basic Astronomy Lesson that the Ground Hog does! You can learn all about the apparent movements of the Sun and the analemma. It's called the Sun Tracker and you can purchase one right from this website.

<span data-mce-type="bookmark" style="display: inline-block; width: 0px; overflow: hidden; line-height: 0;" class="mce_SELRES_start"></span><span data-mce-type="bookmark" style="display: inline-block; width: 0px; overflow: hidden; line-height: 0;" class="mce_SELRES_start"></span> Let's do some Physical Astronomy. The experience will help you to understand the movement of the earth and sun through the seasons. You will build a scientific instrument that is also a fun garden decoration and you will be able to track the Groundhog's Shadow all Spring!

Setup and Process

Start with this cutout pattern and attach it to a post made of metal, wood, or plastic.

Materials

Foam core or construction paper
Scissors or hobby knife - foam core
Wooden or plastic stick 12-24"
Tape or glue for connecting Groundhog
Permanent Markers or weather proof paint for decorating (Groundhog will stay outside)

Help the Groundhog find its shadow

On a sunny day at noon (near to Groundhog Day), stake the Groundhog in the ground and mark where the sun shines through the hole.

Time goes by

Every week or so, the sun will climb higher in the sky and the groundhog's shadow will get shorter. You can visit the shadow tracker weekly and add a new marker each time. You will see the shadow getting shorter and shorter.

A new star will appear in the sky in 2022

Tue, 24 Jan 2017 22:01:52 GMT

An amazing thing is about to happen! A Star in a Star will be born.

EDIT (Nov. 19, 2021): It turns out that the underlying observation data had a timing flaw that makes it "unlikely" that the new star will be born in 2022. See this Wikipedia page about the new Star for more information.

You can witness the birth of a new star in the night sky. The new Star already has a birthday: 2022!

According to scientists, the new star will form when two stars that are orbiting each other grow so close that they merge into one.

The new star will appear in the constellation Cygnus. You can see the approximate location marked by a red circle in the Stellarium screenshot here:

The image of the two blue stars on the home page of this Star in a Star site shows what scientists think it looks like now. This impressive video shows an artist's rendering of the star merge.

In the pair, one star is larger than the other so in the end, there will be a new star... A Star in a Star.

Sidereal time is weird

Sun, 22 Jan 2017 22:49:23 GMT

When does a cycle complete? It all depends on your frame of reference.

Read more: Star Noon and Sun Noon — a 3-part series on sidereal time.

The Moon Dance - Learn Moon Phases

Tue, 17 Jan 2017 14:09:25 GMT

PHYSICAL ASTRONOMY BY DANIEL CUMMINGS

Learn the Moon phases by doing an easy dance. At sunset. Face the sun. Point your right hand toward the Sun. Now point your left hand toward the Sun. Both hands should be pointing at the sun. Now, turn a little bit to the left, keeping both hands pointing at the sun. Swing your left arm out until it is pointing in the opposite direction from the sunset. Bring your hands together again and repeat this swinging motion. Bring your hands together again and point them both at the sun. This time, instead of swinging, bounce your left hand, leftward, some number of times... (14 is perfect if you can do it) ...until it is pointing in the completely opposite direction from the Sun at sunset. Your left hand should now be pointing East. Was the moon at any one of those 14 hand bounce spots? That is the age of the moon in days. Please post your questions in the comments!

Stellarium - a Gift to Humanity

Wed, 11 Jan 2017 22:36:45 GMT

Hello! Find out more about Stellarium in this tutorial that introduces several of the cool and clever things this astronomy software can do. An image of the winter sky showing the Full Moon near the constellations Orion, Taurus, the Big Dog (with the bright star Sirius), and the Little Dog (with the bright star Procyon). Stellarium - a glorious gift to Humanity in software form - gives you super powers. And best of all ... It's FREE!

Superpowers!

Always wanted to know the names of the stars and constellations? You can search, play, pan and zoom, examine, compare and anchor your knowledge. It's a cloudy night? No problem. You can see through the clouds! Wished that the sky had labels on everything? Stellarium has 10 different label types. Stop time? Move time by day, by week? Do you want to see what will happen in 2 months? Or look at the sky during the Pharoah's reign? You can time travel. You can easily drag and zoom, stop time, go in reverse, make a timelapse, follow the moon through its phases. You have a tool to help you understand the ecliptic and sidereal time and retrograde motion. You can see the great orbital swing of Venus as it circles the Sun. Ok! I'm convinced by your Stellarium review. What should I do now? What's my call to action?

Get a copy of Stellarium.

You can download it here. Stellarium is a free, easy to use, and powerful tool - and best of all (did I mention this already?) it's FREE and easy to use. I will write some specific tutorials about my favorite parts of Stellarium in 2017, but for now... go get it and play! You will be able to see things about sky objects and movements that are impossible to see live. But, once you have seen them with the help of Stellarium, the sky will open up for you - like a gift.

Comments

Pingback: […] All images in this listing are generated using Stellarium and show what the sky looks like approximately 8pm on Earth Day April 22nd, 2017 in the Northern […]

Pingback: […] to do Physical Astronomy? Stellarium is the perfect tool for you. It helps you learn to see patterns in the sky. In this article you […]

Pingback: […] if you want to see a version of this image showing the way the real planets are arranged, you can grab a copy of Stellarium. You can set Stellarium to show you the planet orbit […]

What Looks Like Sunset

Tue, 03 Jan 2017 22:14:27 GMT

Is what looks like sunset really the sun - "setting"?

What is that thing that happens every day that makes it look like sunset?

Can you change your mind easily? Are you flexible enough to understand that the same set of observations and facts can lead two different people to two different conclusions?

For a long time, everyone on the Earth thought the Sun was moving and the Earth was staying still. This is just what it looks like and anyone who dared to suggest a different view might easily be considered odd, or worse, dangerous. Having the benefit of hundreds of years of scientific evidence and wisdom to back up my observations, I now have the luxury of believing that it is the Earth that is moving and that the Sun is the one standing still.

It is fun to imagine being carried through space on the surface of a giant ball. Definitely better than staying still while the sun careens through the sky each day. With this image in my mind, I feel the Earth is carrying me away from the view of the Sun.

Sunset should be called "away sun" and not "sun set" because it is me moving, not the sun. It is me being carried away into the shadows forming behind the bulge of the Earth, not the Sun setting. I am riding the Earth with its great round bulk between me and the Sun.

It's NOT a sunset but me... rushing backwards... at 1000 mph as the bulge of the earth grows in between.

I propose "awaysun" as the new name for sunset and "towardsun" as the name for sunrise. These new names help solidify the idea that we are the ones moving.

What do you think?

Comments

Pingback: […] words obscure the truth of our trip around the Sun. We are on the Earth, the Earth is spinning; the Sun appears to be moving, but it is us […]

Pingback: […] you see the Sun “rising” in the morning at dawn you are facing the […]

A Mouse in Moonlight - Illustrations in Goodnight Moon

Sun, 01 Jan 2017 06:00:35 GMT

A Child's Book

Goodnight Moon book cover

As a dad, I treasure a well-crafted, uplifting gem of a book like Goodnight Moon by Margaret Wise Brown, Pictures by Clement Hurd. It's the kind of children's book that just feels good to read out loud to your kids. Plus, the illustrations in Goodnight Moon offer a secret puzzle for the attentive reader - or if you, like me, have read the book 1001 times and you find your tired eyes wandering over the pages.

Beyond Brown's lilting, hypnotic phrasing, and her clever and funny rhymes, the mouse, lighting, and moon illustrations by her partner Clement are even better than you knew! The drawings (more than most other children's books) accurately reflect the real world changes happening over the time it takes the bunny (child) to fall asleep: the clock's hands advance in believable increments, the moon rises and illuminates different areas of the room, and the mouse explores.

Good Moon Rising

Full Moon at 7:40p

This site profiles and dissects Hurd's eminently likable line drawings and discovers a rare and captivating attention to moon detail. Here is a master of children's illustration deploying the highest level of observational, scientific knowledge and gifting it to children (and their bleary-eyed) parents down through the ages.

Next time you find yourself "In the great green room"... take a closer look at the illustrations in Goodnight Moon and witness an intricately interwoven story being told in miniature; silent, like a mouse in moonlight.

Comments

Scott Levine - January 7, 2017 at 10:02 AM

Those small changes in that book are what keeps me going back as a parent. I've always loved that book because of the calming phrasing, but also those small, barely noticeable changes. They're like life and the universe itself. Great post!

starinastar - January 7, 2017 at 11:26 AM

Thanks for the feedback Scott!

The Moon Moves Toward the Dawn - a Mnemonic

Mon, 26 Dec 2016 18:30:05 GMT

Memorize this mnemonic: The moon moves toward the dawn. This phrase describes the day-by-day movement of the moon. With this simple phrase, you can understand the phases of the moon. You will actually begin to see the moon's beautiful orbit traced out in the sky.

Repeat. The moon moves toward the dawn. The moon moves toward the dawn.

The moon moves toward the dawn. It rises higher in the dusky sky after each day. It sweeps over the hills. It circles and rolls. It transits. It leaves the Sun, then chases the Sun. The moon moves toward the dawn. Look East! That's where the moon wants to go. Once arrived, it crosses the face of the Sun and once again moves toward the dawn. The moon moves toward the dawn.

Comments

Pingback: […] answer is that the moon moves toward the dawn. Its orbit around Earth makes it appear to move eastward through the […]

Hello world! Welcome to Physical Astronomy.

Tue, 20 Dec 2016 01:10:00 GMT

Welcome to Star in a Star!

There are many ways to learn about Astronomy and the sky. Some people learn best by reading books or websites. Some learn best by debate and discussion. Some learn by doing.

I like to learn about Astronomy by interacting with people, places, and things. I like to listen to children's questions and wonder along with them. I like to create immersive real-world experiences - aka "Physical Astronomy" - that help to illuminate the answers - when there are answers - and create tools for thought and imagination.

In posts and pages and links and media I am going to show you how to learn (and teach) Physical Astronomy in this unique way. We will learn about how to foster deep scientific understanding through exercising a sense of place and presence in a space.

Most importantly, I hope to share my passion for Astronomy and share the joy I feel each time someone near me says those epic words of discovery: "Wow - I never knew that before."

Daniel