Coma (cometary)
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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.
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