Comets

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, comets, earth, particles, tail, sun, space, material, icy, rocky, outer, orbit, nucleus, miles, meteors, head, halley's, dust, 1910, travel, time, theory, per, path, parts, partly, observed, near, meteorites, metallic, materials, look, long, light, interstellar, halley, found, formed, diameter, cent, called, bright, believe, 1456, years, without, water, travels, together, tiny