Coma (cometary)

From Wikipedia, the free encyclopedia

This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (December 2008)

In astronomy, a coma (from the Latin word for "hair") is the nebulous envelope around the nucleus of a comet. It is formed when the comet passes close to the Sun on its highly elliptical orbit; as the comet warms, parts of it sublimate.

Comets may be more than just simple conglomerations of ice, dust and gases.^[1]

Larger charged dust particles are left along the comet's orbital path while smaller charged particles are pushed away from the Sun into the comet's tail by light pressure.

This gives a comet a "fuzzy" appearance when viewed in telescopes and distinguishes it from stars. Stardust was a NASA mission to recover samples of a comet's coma.

In some cases, such as the Great Comet of 1882, a comet develops a visible antitail or dust tail, which points in a different direction and when the viewing angle and parallax are just right may appear to point in the opposite direction from the normal ion tail.

[edit] See also

• Comet nucleus
• Extraterrestrial atmospheres

[edit] References