A comet is basically a ball of ice and dust that looks like a star with a tail.
Some comets do not have tails, looking like hazy, round spots of light.
A comet is a small body in the solar system that orbits the Sun and (at least occasionally) exhibits a coma (or atmosphere) and/or a tail – both primarily from the effects of solar radiation upon the comet’s nucleus, which itself is a minor body composed of rock, dust, and ice. Comets’ orbits are constantly changing: their origins are in the outer solar system, and they have a propensity to be highly affected (or perturbed) by relatively close approaches to the major planets.
Some comets are moved into sun grazing orbits that destroy the comets when they near the Sun, while others are thrown out of the solar system forever. A new comet may be discovered photographically using a wide-field telescope or visually with binoculars. However, even without access to optical equipment, it is still possible for the amateur astronomer to discover a sun grazing comet online.
Most comets are believed to originate in a cloud (the Oort cloud) at large distances from the Sun consisting of debris left over from the condensation of the solar nebula; the outer edges of such nebulae are cool enough that water exists in a solid (rather than gaseous) state. Asteroids originate via a different process, but very old comets which have lost all their volatile materials may come to resemble asteroids.
Historically, comets were thought to be unlucky, harbingers of destruction by anthropomorphic gods, or aliens, against humans. People are programmed to fear the unknown, but through scientific discovery, as with everything else along the way to enlightenment, there is always a physical explanation.
