|a celestial body that travels around the sun, usually in a highly elliptical orbit: thought to consist of a solid frozen nucleus part of which vaporizes on approaching the sun to form a gaseous luminous coma and a long luminous tail|
|[C13: from Old French comète, from Latin comēta, from Greek komētēs long-haired, from komē hair]|
comet [%PREMIUM_LINK%] (kŏm'ĭt) Pronunciation Key |
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.
An object that enters the inner solar system, typically in a very elongated orbit around the sun. Material is boiled off from the comet by the heat of the sun, so that a characteristic tail is formed. The path of a comet can be in the form of an ellipse or a hyperbola. If it follows a hyperbolic path, it enters the solar system once and then leaves forever. If its path is an ellipse, it stays in orbit around the sun.
Note: Comets were once believed to be omens, and their appearances in the sky were greatly feared or welcomed.
Note: The most famous comet, Comet Halley (or Halley's comet), passes close to the Earth roughly every seventy-six years, most recently in 1986.
Cooperative Program for Operational Meteorology, Education, and Training (National Center for Atmospheric Research)