Why does the Moon change shape?

One night the Moon is a round silver ball. A week later it’s a thin curved sliver. Is the Moon really changing shape? No — it stays the same round rock. The magic is all about light.

The Sun lights up the Moon

The Moon makes no light of its own. It shines because the Sun shines on it, just like a ball glows when you point a torch at it.

The Sun can only light up one half of the Moon at a time — the half pointing toward it. The other half stays dark.

We see the lit part change

The Moon is always travelling in a big circle around Earth. As it moves, we look at its sunny half from different angles.

Sometimes we see the whole lit half — a bright full moon. Sometimes we see only a thin curve, called a crescent. Sometimes the lit side faces away and we see almost nothing — that’s a new moon. These changing shapes are called the Moon’s phases.

Always round, always there

So the Moon never really shrinks or grows. We are simply peeking at its sunny side from a new spot each night.

Wonder fact: The Moon takes about a month to circle Earth once — that’s where the word “month” comes from, all the way back to “moon”!