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A comet is a natural heavenly body made up of dust and gases that moves in an orbit around the sun. Comets can be spotted for varying amounts of time from the earth.
A comet far from the sun is made up of a thick solid body bodies called the nucleus. As it approaches the sun the nucleus becomes wrapped by a bright reflection of dust and gases called the coma. As it approaches the sun, it produces "a tail" which can flare out away from the sun as much as 100 million miles or 160 million kilometers.
Near the sun a comet can change a great deal in size and shape. The comas of comets vary widely in size, some being as large as planets. However, the nucleus, which makes up virtually all a Comet's mass or is much smaller.
Comets lose particles and brightness with each time it passes near the sun. Some of these pieces move around the Comet's orbit as a stream of meteoroids. When the earth passes through this path, a meteor shower is seen.
Scientists do not know what causes comets. They were once thought to have originated outside the solar system; however, modern theories suggest they were formed during the birth of the solar system.
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