Comet tail

A comet tail is a projection of material from a comet that often becomes visible when illuminated by the Sun, while the comet passes through the inner Solar System. As a comet approaches the Sun, solar radiation causes the volatile materials within the comet to vaporize and stream out of the comet nucleus, carrying dust away with them.

Blown by the solar wind, these materials typically form two separate tails that extend outwards from the comet's orbit: the dust tail, composed of comet dust, and the gas or ion tail composed of ionized gases. They become visible through different mechanisms: the dust tail reflects sunlight directly, while the gas tail glows because of the ionization.

Occasionally the relative positions of the Earth, Sun and comet are such that part of the dust tail appears to lie in the sunward direction forming an anti-tail that extends in the direction opposite that of the main tail.

For some comets, larger dust particles that are less affected by solar wind and can persist along the comet's trajectory forming a cometary dust trail that, if it intersects with the Earth's orbit, may produce a meteor shower. Dust trails have mainly been directly observed by spacecraft but in a few instances have been captured by ground-based observers.