Exploring Size, Distance, and Motion

Abstract

Everything we see in the Solar System, and most things that we see beyond it, participate in angular motion, that is to say, motion around a central point or axis. The most important angular motions that we need to understand are rotation and revolution. Rotation occurs when an object spins around an internal axis; revolution happens when an object moves around a point external to itself. When we are speaking about the Earth-Moon system, we must remember that the Earth rotates on its axis, while the Moon revolves around the Earth in its own orbit.