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Comets

A Comet looks like a star with a tail.Some comets do not have tails, and look like hazy, round spots of light.But most comets have three parts;a nucleus, a head, and a tail.The bright central nucleus may be nearly as large as the earth, which is about 7,900 miles in diameter.The head, or coma, surrounding the nucleus, may be from 30,000 to 100,000 miles in diameter.The tail, which look like a bright streak behind the comet, may sometimes be 100,000,000 miles long, or farther than the distance from the earth to the sun.The light of a comet is partly reflected sunlight and partly glow, of particles caused by sunlight.
It has been to believe that comets are masses of tiny solid particles held together loosely by gravitation.But this theory does not fit all the observed facts.Another theory suggest that comets are formed in cold outer space from the interstellar dust particles consisting of such compounds as methane, ammonia, and water, which probably exist as icy particles in outer space.They believe that 70 to 80 per cent of the mass of a comet form those icy particles.The other 20 or 30 per cent is formed from the interstellar dust into rocky and metallic materials such as found in meteorites.This rocky and metallic materials are found in meteorites.This rocky material is imbedded as dust and chunks in the icy material.
As the comet travels in its path, or orbit, it gets near enough to the sun to have the outer layers of the icy material evaporate , due to the heat of solar radiation.Meteors are pieces of stone or metal that fall to earth from space.Theescaping gases and meteoritic material stream off into space along the comets orbit.This release of material accounts for the streams of meteors that are observed when the earth crosses the path taken by certain comets.
Comets travel around the sun in egg-like paths called ellipses. Thetime it takes a comet to make a complete orbitis called i…

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