The verbs revolve and rotate are used in everyday writing to indicate cyclic patterns. For example, revolving debt is debt that is carries over from one credit card statement to the next; crop rotation refers to the successive planting of different crops on the same land. Although they are used as synonyms in everyday writing, this is not so in scientific writing. The difference between the two terms lies in the location of their central axis. If an object is orbiting another object, as the Moon is Earth, then one complete orbit is called a revolution. On the other hand, if an object is turning about itself, or rather, about an axis that passes through itself, then one complete cycle is called a rotation. This difference is epitomized in this statement: Earth rotates on its axis and revolves about the Sun.    1