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.
Larger dust particles are less affected by solar wind and tend to persist along the comet's trajectory, forming a dust trail which, when seen from Earth in certain conditions, appears as an
anti-tail (or antitail) extending in the opposite directions to the main tail.