Phases of the Moon: Why the Moon Seems to Change Shape

0:00Why does the moon seem to change shape from night to night?

0:07The moon travels around Earth about once a month.

0:12The moon makes no light of its own, so sunlight lights it up.

0:17As the moon goes around, the sun lights up the half that faces it.

0:22So one half of the moon is lit, and the other half is dark.

0:27From Earth, we can only see the half of the moon that faces us.

0:32On the sun's side of Earth, the moon's dark half faces us: a new moon.

0:37As the moon moves on, we see more and more of its lit half.

0:42After about a week, we see half of the lit half: a half moon.

0:47A week later, opposite the sun, we see all of the lit half: a full moon.

0:54Then we see less and less of the lit half, until it is a half moon again.

1:01About a month after the last new moon, it is a new moon again.

1:07The sun lights half of the moon, and we see more or less of that half.