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The @stro object for the week of 04/03/2000

image of Comet Hale-Bopp

image (c) 1997 Roger D. Herzler

Comets. Comets are large conglomerations of ice, dust and rock believed to be relics left over from the formation of the solar system and are often compared to "dirty snowballs". Comets are thought to reside in the outer regions of the solar system known as the "Kuiper Belt" and the "Oort Cloud". Their distant orbit around the Sun is sometimes perturbed by the gravity of passing stars or the large gas planets and a comet can subsequently be thrown into our area of the solar system where they are occasionally visible to the naked eye.

In the outer regions of the solar system comets are dormant and appear much like asteroids. When a comet gets closer to the inner solar system it can come to life and develop an active tail. This tail consists of gas, dust, ice and rock which is sloughed off by the heat of the Sun pushed away from the comet by the solar wind. An interesting note is that the tail always points away from the Sun regardless of what direction it is traveling in relation to the Sun.

Comet compositions and descriptions can vary from comet to comet. Some of the chemicals found in comets include methane, ethane, carbon monoxide, and they are also sources of large amounts of water. Comets are thought to have an average diameter of around 3 miles (5 kilometers), but some comets exceed this amount, such as Hale-Bopp which was about 25 mi. (40 km) wide.

There are several current theories that relate to comets. Those with large implications to science include the theories that comets brought water to Earth's surface and could have delivered chemicals essential to life on Earth. Other theories even suggest that comets transport microscopic bacterial life, although no direct evidence for this is currently available.

It was believed for eons that comets influenced human existence as harbingers of doom or predictors of other major events yet to come. In present times comets are not thought to directly affect life on Earth with the possible exception of a cometary impact on Earth, or the observation of various meteor showers left behind by comet tails. However, they are followed intensely for many reasons including their close relationship to the formation of the solar system.

Comets are one of the few astronomical bodies that a person can name for themselves - the discoverer of a new comet gets to name it, so comets are usually named after the person that found them.

Some recent famous naked-eye comets include:
Comet Hale-Bopp (discovered in 1995)
Comet Hyakutake (discovered in 1996)
Comet Shoemaker-Levy 9 (discovered in 1993)
Comet West (1975)
Comet Bennett (discovered in 1969)
Comet Halley (first named in 1682)

more information about comets...

more information about comets from the U. of Michigan...

more about the Kuiper Belt and Oort Cloud...

make a "kitchen comet"...

more on Comet Hale-Bopp...

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