Physics Zone Lesson: Earth-Moon Orbit
A misconception in the relationship between the Earth and the Moon is that the Moon revolves around the Earth. This is not quite right. The Moon and the Earth actually move around or orbit their common center of mass which is called the barycenter. As you can see in the animation below, the barycenter,shown as the red dot, is located about 1/4 of the way to the center of the Earth (~1,700Km below the surface). The barycenter is the center of mass for the Earth-Moon system.
By now you may have guessed that the idea of the Earth revolving around the Sun isn't quite right either. The Sun-Earth system has a center of mass which is not in the very center of the Sun. It is beneath the surface of the Sun but not at its center So the Earth and the Sun actually orbit the barycenter.