A comet is a small, fragile, irregularly shaped body composed mostly of a mixture of water ice, dust, and carbon- and silicon-based compounds. Most comets have highly elliptical orbits that repeatedly bring them very close to the Sun and then swing them into space. They have three distinct parts: a nucleus, a coma, and a tail. The solid core is called the nucleus, which develops a coma with one or more tails when a comet sweeps close to the Sun. The coma is the dusty, fuzzy cloud around the nucleus of a comet, and the tail extends from the comet and points away from the Sun. The coma and tails of a comet are transient features, present only when the comet is near the Sun. (Continued >>)