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The moon is a great traveler. Every month it takes a trip around the earth. In fact the moon never stops traveling. Around and around the earth it goes.

During each of these monthly trips the moon takes around the earth, sometimes it looks like a large circle in the sky; other times it looks like a half-circle facing either right or left. And sometimes there is no moon at all!

What happens to make the moon change like this? Where does it go when it isn't there in the night, big, bright and shining? Is it hiding from us, playing peek-a-boo high in the sky?

The earth is shaped like a great big ball. The moon is a ball too, a smaller ball. Near the moon and the earth is the sun. The sun sends light to the earth, and light to the moon.

As the moon travels around the earth, it gets so far behind the earth that the sun can send light to only part of it. Then we see just that part of the moon the sun lights. And once every month we cannot see any moon at night, called a new moon, when the earth blocks off all or most of the sun's light. That's when the moon seems to be playing hide-and-seek.

But when the moon comes around the other side of the earth, where the sun can shine fully all over its face, we see a full moon.

Look for the moon tonight to see what shape it is. Then watch how it plays hide-and-seek in the sky during the month.