Have you noticed that the moon sometimes seems to grow and shrink? Does it look like a big round ball? Or is it just a sliver of light in the sky? The moon seems to change. But it doesn't really. The moon revolves around the Earth. It takes about four weeks to make the journey, and as it travels around we can only see certain parts of it. Try the simple experiment described inside using an orange, a pencil, and a flashlight, and you'll understand why the moon seems to change.