Moon Phases for Kids: Why Does the Moon Look Different Every Night?
Why is the moon sometimes round, sometimes a crescent and sometimes gone? In the moon lab, kids push the moon around the Earth themselves and see how the moon phases happen. With memory tricks, a lamp-and-apple experiment and moon cookies.
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More for young space fans
Drag the slider, press play or tap a moon on its orbit.
In the Southern Hemisphere the moon is upside down: the waxing moon is lit on the left there.
New moon: The moon is between the sun and the Earth. Its sunlit side faces away from us, so we can hardly see it at all – and it's only in the sky during the day anyway, together with the sun.
Waxing crescent: A thin sliver of the bright side peeks over at us. You'll see the crescent low in the west in the early evening, just after sunset.
First quarter: We look at the moon from the side and see exactly half of its bright side. In the evening the half moon stands high in the sky.
Waxing gibbous: Every day we see more of the sunlit side. It rises in the afternoon and shines until late into the night.
Full moon: Now the Earth is between the sun and the moon, and the whole bright side faces us. The full moon rises when the sun sets and shines all night long.
Waning gibbous: The bright side slowly turns away from us again. It rises late in the evening, and early risers still see it in the morning sky.
Last quarter: Again we see the moon from the side, but this time the other half is bright. It rises around midnight and stands high in the sky in the morning.
Waning crescent: Only a thin sliver is left. You can see it very early in the morning in the east, just before sunrise – and then it all starts again.
The moon doesn't shine by itself
The moon is a huge ball of rock. It doesn't glow like a lamp; the sun shines on it – always on exactly one half, just like on the Earth. On one half of the moon it's daytime right now, on the other half it's night.
While the moon travels around the Earth in about a month, we look at it from a slightly different direction every evening. Sometimes we see a lot of its bright day side, sometimes a little and sometimes only the dark night side. That's how the moon phases happen: from new moon to full moon and back again in 29.5 days.
A common mistake
The moon phases are not caused by the Earth's shadow! The Earth's shadow only falls on the moon during a lunar eclipse. That only happens a few times a year and always at full moon – and then the moon often turns copper red.
The moon spins too – but exactly as fast as it travels around the Earth: once in about 27 days. That's why it always shows us the same face, and nobody on Earth has ever seen its far side. Turn the spin off and see what would happen otherwise.
The marked crater always points at the Earth – we always see the same side.
Without its own spin, we would gradually see every side of the moon.
By the way, the far side isn't dark: at new moon it's bright daytime there.
Memory tricks: is the moon waxing or waning?
The rule of thumb for the Northern Hemisphere: if the right side is lit, the moon is getting bigger – it's waxing. If the left side is lit, it's getting smaller – it's waning.
The DOC trick: a waxing moon looks like the letter D, the full moon like an O and the waning moon like a C. D-O-C, in that order.
The clock trick: if you see the moon in the evening, it's usually waxing. If you see it early in the morning, it's usually waning.
Why can you sometimes see the moon during the day?
The moon isn't only in the sky at night! It rises about 50 minutes later every day on average, so it's often in the sky during the day too, especially around first and last quarter. It's bright enough to show up against the blue sky.
On the other side of the world it's upside down
In Australia, New Zealand or South Africa the moon looks the other way around: the waxing moon is lit on the left there, and the man in the moon stands on his head. Switch the moon lab to the Southern Hemisphere and compare.
Experiment: moon phases with a lamp and an apple
Make the room dark and put a lamp without a shade on the table: that's the sun.
Stick an apple or a foam ball on a pencil: that's the moon. Your head is the Earth.
Hold the moon at arm's length a little above your head and slowly turn around in a full circle.
Keep looking at the apple: you'll see new moon, crescent, half moon and full moon – just like in the sky!
Moon phases you can eat
Twist apart sandwich cookies with white cream and scrape the cream with a spoon so that you get all eight moon phases – from the new moon with no cream at all to the full moon with all of it. Who can put them in the right order? Afterwards the whole lunar cycle may be eaten.
The moon diary
Draw what the moon looks like every evening for a month and write down the date and time. If you can't see it, write that down too. After four weeks you'll have watched the whole lunar cycle yourself – just like a real astronomer.
Questions about the moon
How long does a whole lunar cycle take? From one new moon to the next takes 29.5 days on average. That's where our word month comes from – it's related to the word moon.
How far away is the moon? About 384,400 km (239,000 miles) on average. A car driving nonstop at highway speed would need more than five months to get there, a rocket only three days.
How big is the moon? It's 3,474 km (2,159 miles) across, about a quarter as wide as the Earth. Around 50 moons would fit inside the Earth.
Is there air on the moon? No, almost none. That's why astronauts need spacesuits, why the sky there is black even in daytime and why there are no sounds – not even your own footsteps.
Is the moon made of cheese? No, even though the idea is very old and funny. The dark patches are huge plains of cooled lava, and the holes are impact craters. They look a bit like Swiss cheese, but they certainly don't taste like it.