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Have you ever looked up in the sky and seen a little ball creeping by? If so, did you wonder what it was? That little ball is called a comet. Comets are small, fragile, and irregularly shaped. Most are composed of frozen gas. However, some are composed of frozen gas and non-volatile grains. They usually follow very strict paths around the sun. Comets become most visible when they cross the sun. This also applies to people who view comets with telescopes. When a comet gets near the sun it becomes very visible because the sun's radiation starts to sublime its volatile gases, which, in turn, blow away small bits of the little solid material the comet has.
Another feature of a comet is a long tail. This is caused by materials breaking off and expanding. They expand into an enormous escaping atmosphere called the coma.
This becomes at least the size of our planet. With the comet going so fast, these materials are forced behind the comet, forming a long tail of dust and gas.
Comets are cold bodies. We see them only because the gases they are composed of glow in the sunlight. All comets are regular family members of the solar system family. They are bound by gravity to a strict path around the solar system. Scientists believe that all comets were formed of material, originally in the outer part of the solar system, which did not become incorporated into planets. This material is from when the planets just started forming. This makes comets an extremely interesting topic to scientists who are studying the history of the solar system.
In comparison to planets, comets are very small. They can be anywhere from 750 meters...