GPS uses Quasars

GPS uses Quasars to work

GPS uses quasars to get its own position
GPS satellite in low Earth orbit. Credit: NASA artist’s impression
The 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.

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?

An artist's impression of a quasar. This one is surrounded by water. GPS uses quasars like this one as an anchor point for GPS.
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

Quasar GPS map showing where quasars would be in the sky if you could see them. The celestial sphere locations are indicated by dots on the Aitoff projection.
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.


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 Article 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. General audience description of GPS relationship to quasars with quotes from Chopo Ma from Goddard Space Flight Center. Another general audience introduction with similar quotes from Chopo Ma from Goddard Space Flight Center. A third article quoting Dr. Chopo Ma. This was big news in November 2009 but nobody has written on it much since then. This article has a nice image of the “locations” of the quasars as well as an artist’s impression of that great beast.

More detailed PDF paper direct from the researchers compiling and cleaning the data:

PDF with some recent 2017 writings on making the ICRF even more precise:

Astrometry overview from The University of Arizona:


Blue Moon, Dark Moon, Nose Moon, Tail Moon

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 tinted blue to make it look like the moon is actually blue. A blue moon means 2 full moons in a calendar month.
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.

Blue Moon explanation shows how the moon phase cycle fits inside the larger calendar month. So, we have two full moons in a single 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.

The October 2020 calendar month contains two full moons so the second one is called a Blue Moon.
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.

The October 2018 calendar month contains two last quarter moons so the second one is called a 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.

The Dark Moon is the name for the second New Moon in a month - it's like a Blue Moon

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

The Nose Moon is the name for the 2nd Last Quarter Moon in a month - it's like a Blue Moon

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

The Tail Moon is the name for the second First Quarter Moon in a month - it's like a Blue Moon

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


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.


* 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.


Wikipedia page on Lunar Phase

Astronomy Koan

Astronomy Koan – Definition

A family views the visible orbit path of the earth.
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

Welcome Starry Night event visitors! We will build this fun, interactive model of the merry-go-round Earth on the evening of March 3rd, 2018 around a real campfire. Read on for the background and teaching method.

The Earth is like a Merry-Go-Round

Merry-Go-Round Earth model demonstrating how the seasonal constellations work
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.Click here to continue reading…

Stellarium – Find the Humanity Star

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:

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.

You can track the position of the Humanity Star with 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 panels showing the satellites plugin which is needed to track the Humanity Star (it is a satellite after all)
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”

Stellarium can hep you find the Humanity Star
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.

Stellarium search panel showing the Humanity Star as a findable object
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
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.

This table shows the visibility and brightness prediction for the Humanity Star satellite
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.

Quiz – Can we see the Sun at midnight? Where is it?

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.

Image of the Sun's rays hitting the Earth. The Earth is tilted 23.4 degrees. Summer is when the northern hemisphere is titled toward the Sun. The summer Sun never sets - not even at midnight - if you are north of the Arctic Circle.
You can see the Sun at midnight! If you are at the North Pole in summer.

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?

Looking north or south to see the Sun at midnight?
A compass rose showing the cardinal directions.

Click here to continue reading…

“Star In a Star” Translated into 90 languages

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 providing translation of Physical Astronomy teaching material to a global language audience
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

Physical Astronomy – Definition of a New Way of Teaching

Definition of Physical Astronomy

Physical astronomy definition using Leonardo DaVinci's Vitruvian Man drawing surrounded by moon phase images
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.

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.


Moon Phase Emojis – A Review

Moon Phase Emojis – and other space emojis

Emoji designers created a nice range of astronomy emojis and space emojis.  My favorite emojis are the Moon Phase Emojis. Here is a listing of all of the space emojis as seen on Apple’s Mac “High Sierra” OS.

All of the astronomy and space themed emojis in one image
All of the astronomy and space themed emojis in one image

Space emojis to copy (these look different on each browser)

Here are the same emojis as shown in the image above, but shown as real emojis that can be selected individually and copied.

👩‍🚀 👨‍🚀 🌎 🌍 🌏

🌕 🌖 🌗 🌘 🌑 🌒 🌓 🌔

🌚 🌝 🌞 🌛 🌜 🌙 💫 ⭐ 🌟 ✨

💥 ☄ ☀ 🌈

🚀 🛰

🗺 🎑 🌅 🌄 🌠 🌇 🌃 🌌

📡 🔭

☪ ✡ 🔯

🔅 🔆 🌐 🌀 *️⃣ 🎴

♈ ♉ ♊ ♋ ♌ ♍ ♎ ♏ ♐ ♑ ♒ ♓

✳ ✴ ☾ 〰 ➰ ➿

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 - 3d, yellow, cratered, and glowing
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 Mac Computers - flat, orange, spotted, cartoon.
The Full Moon emoji as seen on Windows PCs.


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



See Mercury and Venus orbits during the day

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.

Use your hands and elbows to see Mercury and Venus orbits any time of day or night. The orbits of Mercury and Venus can be seen.
Two hand spans show Mercury’s orbit, elbows show Venus’s orbit.

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.

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Shapes with Shadows – astrosketching Moon features with Alex Massey

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.

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Galaxy Rise

Physical Astronomy by Daniel Cummings

A still more glorious dawn awaits Not a sunrise, but a galaxy rise A morning filled with 400 billion suns The rising of the milky way.

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.

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Super Moon December 3rd, 2017

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 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.

Supermoon arrangement of moon's orbit around the Earth
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.

Walk to Mintaka

Physical Astronomy by Daniel Cummings
Mistakable rises toward the zenith as you walk toward the equator
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. Click here to continue reading…