Saturday 3 January 2009

C O M E T S

Q: How are comets formed?

A: There are two main theories about how comets are formed. According to one theory, as the Sun moves through clouds of interstellar dust, its gravity pulls the particles together to form a dense stream that trails behind the Sun like the wake of a ship. Occasionally, an enormous clump of particles is drawn towards the Sun to become a comet. According to the other theory,t he Sun's planets are surrounded by a permanent whirling cloud of particles containing billions of clumps, a cloud that extends halfway to the nearest star. The gravitational influence of nearby stars deflects the path of a clump, causing it to swing close to the Sun and become visible on the earth as a comet. Comets have no trails until they get close to the Sun. When they come closer to the Sun the intense heat vapourises portions of them and the gas blows out to form a glowing, smoke like streamer. The tails vary enormously in shape and size. Because a comet loses part of its substance every time a tail is formed, it is sure to burn itself out eventually.

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