When people first began to think about orbits, they thought that all orbits had to be perfect circles, and they thought that the circle was a "perfect" shape. Copernicus and Galileo, for example, thought so. But when people began to study the motions of planets carefully, they saw that the planets were not moving in perfect circles. Some of the planets have orbits that are almost perfect circles, and others have orbits that are more oblong (egg shaped).