Comet tail
A comet tail and coma are visible features of a comet when they are illuminated by the Sun and may become visible from Earth when a comet passes through the inner Solar System. As a comet approaches the inner Solar System, solar radiation causes the volatile materials within the comet to vaporize and stream out of the nucleus, carrying dust away with them.
Diagram of a comet showing the dust tail, dust trail (or anti-tail), and ionized gas tail, which is formed by the solar wind flow.
Blown solar downwind, two separate tails are formed: one composed of dust and the other of gases. They become visible through different phenomena: the dust reflects sunlight directly, and the gases glow from ionization. Most comets are too faint to be visible without the aid of a telescope, but a few each decade become bright enough to be visible to the naked eye.
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