Moon Phases Names – an easy way to remember

The 8 Moon Phases Names

Here are the “official” 8 Moon Phases in order:

  1. New – the new moon is not visible
  2. Waxing Crescent – the Moon starts growing
  3. First Quarter – the moon looks like half a circle
  4. Waxing Gibbous – still growing
  5. Full – we see the entire circle of the Moon lit up
  6. Waning Gibbous – the Moon starts shrinking
  7. Third Quarter – again only half a circle is visible
  8. Waning Crescent – the Moon is about to disappear
  9. New (again) – the new Moon is not visible 
The Moon Phases names in the correct order showing the progression from new moon, through waxing moons, to full moon, then back down through waning moons, to new moon again in a cycle
The Moon Phases in order with official names.

The moon phases names are odd

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:

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 Hat will help you learn the Moon phases names

If you can get your hands on a Moon Hat (a great science gift made by Star In A Star), you can learn all about the Moon phases every time you wear the hat.

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.

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

Here’s a good way to remember the order of the Moon phases: 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).

Moon phases names in order make the shapes of the letters DOC in order - it's a good mnemonic to remember the phases of the Moon and whether it is waxing or waning

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.

  1. The cycles repeat – New to Full to New (again).
  2. 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?
  3. The New Moon is the commonly accepted “beginning” and also the “end” of the cycle.
  4. Gibbous is a really weird word – it is from the Latin “hunch or hump.”
  5. There is a first and third quarter, but no 0th or 4th quarter.
  6. 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 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.

8 Ways to Find the North Star

Find the North Star

Can you find the North Star in this image? It is the star that is closest to the middle of the concentric rings of star trails. This is a long exposure photograph of real stars as seen over the course of several hours during the night.
A long exposure photograph showing all of the other northern sky stars circling around the North Star. Image provided by ESO.

You can use these 8 ways to find the North Star (Polaris).

But, first, 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.”

You can find the North Star using the two pointer stars of the Big Dipper (Dubhe and Merak) The North Star is also called Polaris and is part of the constellation Ursa Minor.
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 and 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 long exposure of circumpolar stars as viewed from near the North Pole.
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.

8 ways to find the North Star

  1. 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.
  2. 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.
  3. 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.
  4. 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.
  5. 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.
  6. 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.
  7. The North Star is located in between the two easy-to-identify constellations The Big Dipper and Cassiopeia – the Queen.
  8. 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.

Myths about the North Star

  1. “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.
  2. “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.
  3. “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?

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.

IMAGE of floating/flying things overhead (in roughly size order) that can block all or part of the SUN: Flying animals (Bugs, Birds/Flying Mammals), Flying objects (Drones/Balloons/Airplanes/Helicopters/Rockets/Bombs/Blimps), Smoke/Clouds, Spacecraft (Satellites/Space Stations/UFOs), Asteroids, Moon, Mercury, Venus, Earth.
Wondering “Where is the Sun?” These are 10 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.Click here to continue reading…

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.

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. Click here to continue reading…