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Hands-on activity: Cookie Moon phases
The mission
Make a toy model of the Earth-Moon-Sun system using cookies, then use it to explain the phases of the Moon.
Requires eating cookies as you go!
Age range: 9-12
What you’ll need:
- Creme-filled sandwich cookies (1 pack)
- Lamp or flashlight
- A fist-sized object that isn’t fragile, like an apple or tennis ball
- A smaller object that isn’t fragile, like a blueberry
- Butter knife
NGSS compatibility (for U.S. teachers):
Disciplinary Core Ideas: 5-ESS1-1, 5-ESS1-2, and MS-ESS1-1.
Science & Engineering Practices: developing and using models; constructing explanations; engaging in argument from evidence.
Crosscutting Concepts: patterns; systems and system models; cause and effect.
Background
The phases of the Moon is one of the most important — but difficult — concepts that kids confront as they begin to learn about space. To see why the Moon’s appearance changes from day to day, children have to understand how the Moon moves relative to the Sun and Earth. This is a complicated mental picture. But once someone has confidence with it, they’ll be rewarded with a practical grasp of one of the most beautiful and easy-to-see astronomical objects. Afterward, a child can go on to learn about the rest of how the Solar System moves and changes through the night sky.
1
Place the lamp/flashlight in the middle of a table and turn it on. Put the fist-sized object about a foot away, to the right. If you’re using a flashlight, point it the same direction.
- The light represents the Sun, and the smaller object is Earth. You’re looking at both from a “bird’s eye” view.
- Now, place your small object at a 12 o’clock position relative to Earth. This represents the Moon.
2
Look at your Moon. Because of your Sun/lamp, it should be half lit up and half in shadow (if it isn't, make your light brighter or your room darker). From Earth, how much of the lit-up part of the Moon would you see?
- Bring your eyes alongside your Earth on the table to check.
- Twist a cookie apart and lick off part of the filling on the creamy side so that it matches what you see. If it’s hard to get the filling looking just right, use your butter knife to scrape it off.
- Place that cookie between your Moon and Earth. This is a half moon. It’s also called the first quarter Moon, because it is one-quarter of the way through a Moon’s cycle of phases.
It’s never daytime on Earth everywhere at once. At almost any given time, half of our planet will be lit up — the side facing the Sun — while the other half faces away and stays in nighttime shadow. The same thing is true of the Moon. Here, someone on Earth would see the Moon half in shadow and half lit up.
3
Leaving the first cookie where it is, move your Moon to a 3 o’clock position relative to Earth. How much of the lit-up part of the Moon would you see from Earth now?
- The answer should be: all of it.
- Twist another cookie apart and place it between your Earth and Moon so it matches what you see. This is a full Moon.
- This time, to match the Moon, your cookie should still have all of its filling.
🌕 Why doesn’t Earth block the Sun’s light from reaching the full Moon?
The Moon’s orbit around the Sun is slightly tilted compared to Earth’s, so we have to think in 3D. Lift the full Moon cookie off the table a few inches — during most full Moons, the Moon is “above” or “below” Earth, like this, so Earth doesn’t block the Sun. Sometimes, things do happen to line up perfectly, and then Earth’s shadow crosses the Moon. This is called a lunar eclipse.
4
Leaving the last cookie where it is, move your Moon to a 6 o’clock position relative to Earth. Now how much of the lit-up part of the Moon would you see from Earth?
- Twist a cookie apart and place it between your Earth and Moon so it matches what you see. This is another half moon.
- To match the Moon, your cookie should have half its filling eaten this time. The white semicircle of creme should be facing the left, toward the Sun.
- Explanation: This is also called the third quarter Moon, because it is three-quarters of the way through a cycle of phases. It might seem weird that it looks the same as the half Moon in Step 2, but remember: we’re seeing things from a “bird’s eye” view, as if looking down from far above Earth’s north pole. If you were standing on Earth, the two half Moons would look different. The one in Step 2 would appear lit up on its left side, and the one in this step would be lit up on its right side.
5
Move your Moon to a 9 o’clock position relative to Earth. Twist another cookie apart and, like in the last couple steps, prepare it so it matches what the Moon would look like from Earth.
- Here, that should mean eating all the filling so your cookie is licked clean.
- Now the side of the Moon that's lit up by the Sun is facing away from Earth. From our planet, we would only see the part of the Moon that’s in shadow, so the Moon would look completely dark.
- This is called a new Moon.
- Again, you can lift the new Moon cookie off the table a few inches to show why it doesn’t block the Sun’s light from reaching Earth — except during the rare times that the Sun, Earth, and the new Moon all line up perfectly, causing a solar eclipse.
6
Move your Moon to a 10 o’clock position relative to Earth. Twist another cookie apart and, like in the last couple steps, prepare it so it matches what the Moon would look like from Earth.
- Here, that should mean eating all the filling except for a crescent shape.
- Make sure your crescent is tilted so its angle matches the light you see on your Moon.
- When the side of the Moon we see from Earth is getting more and more lit up from day to day, we say the moon is “waxing.”
7
Move your Moon to a 2 o’clock position relative to Earth, then repeat the previous steps.
- This is a “gibbous” Moon, meaning that the side we see from Earth is more than half (but not completely) lit up.
8
Move your Moon to a 4 o’clock position relative to Earth and repeat the previous steps to place a matching cookie.
- Then move the Moon to do a 7 o’clock position and place one last matching cookie.
- When the side of the Moon we see from Earth is getting less and less lit up from day to day, we say the moon is “waning.”
Admire your Moon phases!
Now we know what causes the Moon’s phases: depending on where the Moon is relative to the Sun and us here on Earth, we see more or less of the side of the Moon that the Sun is shining on.
Check out the answers to some common questions about the Moon, like why the Moon looks the way it does, why Earth has a moon in the first place, and what supermoons are — or, check out our eclipse activity guide for more hands-on space stuff!