A celestial object that orbits the Sun along an elongated path. A comet that is not near the Sun consists only of a nucleus-a solid core of frozen water, frozen gases, and dust. When a comet comes close to the Sun, its nucleus heats up and releases a gaseous coma that surrounds the nucleus. A comet forms a tail when solar heat or wind forces dust or gas off its coma, with the tail always streaming away from the Sun.♦ Short-period comets have orbital periods of less than 200 years and come from the region known as the Kuiper belt. Long-period comets have periods greater than 200 years and come from the Oort cloud. See more at Kuiper belt Oort cloud. See Note at solar system.

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