The moon does not really change shape. It is always a ball. We see a different amount of its sunlit side as it orbits Earth, which takes about a month. When we see all of the sunlit side, it is a full moon. When we see none, it is a new moon.
Peabody: Hi, I am Peabody! Some nights the moon is a big circle. Other nights it is a thin curve. Is the moon changing shape? No! These looks are called phases.
Crumb: I am Crumb! The moon does not make light. It is a big round rock. It shines because it reflects light from the sun, like a mirror.
Peabody: The sun always lights up half of the moon, the half facing the sun. The other half is dark. This does not change.
Crumb: The moon goes around Earth. One trip takes about a month. As it moves, we see more or less of the lit half from here.
Peabody: When we see all of the lit half, it is a full moon. When the lit half faces away from us, we cannot see it, and that is a new moon.
Crumb: In between, we see slices. A thin curve is a crescent. Half a circle is a quarter moon. Then the cycle starts again. Look up tonight and see which phase it is!
Crumb: Here is a recap! The moon reflects sunlight, and half of it is always lit. As it orbits Earth, we see more or less of the bright half. That is why we have phases!
Quiz: five questions
Tap an answer. Stuck? Tap the hint. Nothing is scored or saved.
Question 1 of 5
Does the moon make its own light?
The words
phase
how much of the lit moon we see
reflect
to bounce light back
crescent
a thin curved slice of the moon
orbit
the path the moon takes around Earth
full moon
when we see the whole lit side of the moon
Make it: put the explainer in order
Tap the scenes in the order they happen. Which comes first?
Try it without a screen: Moon in the lamp
You need: a lamp with no shade, a white ball or orange, a dark room.
Hold the ball at arm's length. The lamp is the sun.
Turn slowly in a circle, keeping the ball in front of you.
Notice when you see a full lit face, a half, a thin curve and almost none.
Draw the four shapes you saw.
For the grown-up
This explainer shows the moon phases as the changing view of one lit half, not Earth's shadow (a common slip: that is an eclipse). The lamp and ball activity builds the right picture. A moon diary of a week of evenings is a good follow-up. Nothing here is saved or shown to anyone.