Davy Buddin, age 9, of Olanta, South Carolina, for his question:

Why can't we call the moon a planet?

Our golden moon is as big as a small planet    but size has nothing to do with it. The secret lies in how it goes around the sun. If the moon were a planet, its orbit around the sun would be one smooth line. This is how the Earth goes around the sun    and the Earth is a planet. But not the moon. It dances around a lot of curlicues as it goes.

Actually it loops around and around the Earth    and the two of them go around the sun. This is because the moon is captured by the earth's gravity, and the pull of gravity will not let it escape. It has to orbit around us, making curlicues as we travel together around the sun. Because this is so, we say that the moon is a satellite of the planet Earth.