What is a comet?

Since 1995 their have been 878 comets that have been cataloged. Comets are called dirty snow balls or even icy mud ball. They are small and fragile irregularly shaped bodies that have have mixtures of ices (both water and frozen gases) and dust that did not go into the planets when  the solar system was brought together. These highly elliptical orbits bring them very to the sun as they swing deeply into space.

How do comets travel?

After about 500 passes close to the sun. Almost all comets ice and gas is lost leaving dry and rocky objects just like a asteroid in appearance. Comets are invisible but, not when there near the sun. Almost all comets have highly eccentric orbits which go much farther back then Pluto. Halley comet is named after Edmond G. Halley. Edmond G. Halley was the first person to suggest that comets were a natural parts of the solar system around the sun. He also suggested Halley comet comet is a common visitor. That returned every 76 years and was the same one from recent history that had come the years of 1531, 1607, and 1682. Edmond G. Halley also predicted that Halley's comet would return in 1758. Edmond G. Halley died in 1742 and did not live to see his comet return March 1759. With a bright appearance.

Mathematical theory suggests that comets come to our solar system from far far away even as far as 1000,000 earth to sum distances. Comets come to our solar system from all different directions. The place comets come from is a giant sphere surrounding our solar system. This sphere is called the Oort Cloud which was named after Jan Oort. The Oort cloud existed since 1950. Other comets may come from a closer in. This place is called Kuiper belt which is past Pluto orbit.

When was the 1st comet discovered?

Most comets were first discovered by a astronomer. Since comets are at their brightest when  near the sun they  are only visible at sun rise or sun set. Most recorded history of comets played a unique role in science history but, it was really only about 50 years ago. In 1968 we got a close up picture of comet Halley.

How are comets made?

Comets are the most primitive bodies in the solar system. Some of the material inside a comet is preserved in nearly the same state it was in when the solar system was just taking shape, before the Sun and the planets were fully formed. Each comet is a sample of the building blocks present in the  solar system the  solar nebula at the time the comet was formed, about 4.5 billion years ago. Although the  material may have undergone changes before it was incorporated into the comet, very little has been change since. A comet is literally a little piece of the past.

In general, we believe that comets begin to form by an gathering "snowball" effect in which the icy dust grains stick together to form fractal-like aggregates. This process begins at some considerable distance from the center of the solar nebula, perhaps as far as 100 astronomical units (AU) away.  At this stage, the movements of the dust grains and the small aggregates are coupled to the movements of the  nebular gas.  As the cometesimals fall closer to the center of the solar nebula, they continue to grow by the increased accumulation of ice and dust grains, as well as by merging with other aggregates in their path. In due course this pile of rubble becomes a comet, perhaps 10 to 20 kilometers across, which contains a collection of materials from a wide swath of its orbital radius.

Estimates of how long it takes to build a comet in this way depend partly on the size of the solar nebula in which the comet forms. In one model, Stuart Weidenschilling of the San Juan Capistrano Institute has shown that a good-sized comet could be made in about 100,000 years.

Credits:
http://www.americanscientist.org/template/AssetDetail/assetid/22746/page/2;jsessionid=aaa5LVF0

http://www.kidsastronomy.com/comets.htm

http://www.windows.ucar.edu/tour/link=/comets/Oort_cloud.html

http://www.nasm.si.edu/research/ceps/etp/comets/

http://www.nineplanets.org/comets.html

http://can-do.com/uci/lessons98/Comets.html

http://www.enchantedlearning.com/subjects/astronomy/comets/cometorigins.shtml

http://csep10.phys.utk.edu/astr161/lect/comets/halley.html

http://www.pbs.org/wgbh/nova/spacewatch/weaver.html

Halley Comet Picture: http://csep10.phys.utk.edu/astr161/lect/comets/halley.html

Comet Picture: http://www.nineplanets.org/comets.html