ELI5: Why does the moon change shape?

Imagine you're playing hide-and-seek with a ball (that's our Moon!). Your friend has a flashlight (that's our Sun!).

• Your friend always shines the flashlight on one side of the ball.
• You walk around the ball.

Other times, the ball is between you and the flashlight, so you don't see any light – that's a New Moon! It's there, but it's dark.

And sometimes you only see a slice of the bright side, like a crescent. That's because the ball is partly lit, and you only see the lit part from where you're standing. That's when we see phases like a Half Moon or a Crescent Moon.

The Moon doesn't actually change shape. It's always a ball. It just looks like it's changing shape because we see different amounts of the lit-up side as it goes around the Earth. The Sun is always shining on half of the Moon, but we only see what's facing us. So, it's just a matter of perspective! Like looking at a friend with half their face in the shadow - they haven't changed, just the light on them!