Coma (Astronomy)

It has been suggested that this article or section be merged with comet. (Discuss)

A Coma is a spherical cloud of material surrounding the head of a comet. This material is mostly gas that the Sun has caused to boil off the comet's icy nucleus. This gas shines both by reflected sunlight and light emitted by excited molecules. A cometary coma can extend up to a million miles from the nucleus.