Comets are some of the most spectacular objects in the night sky. About once per decade, a truly bright comet comes along and can be viewed by the unaided eye. Where do these comets come from? Where do they spend most of their lives?

Some comets orbit the Sun once every thousand years or so and can be easily viewed only when they are in the inner solar system. These are known as long period comets. Nonperiodic comets appear in the inner solar system only once. Some comets, however, enter the inner solar system repeatedly and predictably. These are the short period comets.

SOURCE: Adapted from the Space Telescope Science Institute, PR-95-26, created June 14, 1995.

All of these comets are in orbit around the Sun but, unlike the planets, which all revolve around the Sun in the same direction and are confined to approximately the same...