Comets are small Solar System bodies that are caught in the Sun's orbit. When a comet is close to the sun they exhibit a visible coma, otherwise known as a tail, which effects the solar radiation from the comet's nucleus. Comet nuclei are made up of loose collections of ice, dust, and small rocky particles.
The orbit of a comet ranges from a few years to hundreds of thousands of years. Some comets flow through the Solar System once before being thrown out into interstellar space. Short period comets are thought to be created in the Kuiper belt (which is associated with the scattered disc) while long period comets originate at a great distance from the sun, perhaps in the Oort cloud. These comets are thought to be made of debris left over from the condensation of the solar nebula. Comets are thrown into the inner solar system by the gravitational push of other stars.
The trail of debris following comets is what shows as a comet's path crosses the earth's path. A meteor shower occurs every year between August ninth and thirteenth when the Earth passes through the orbit of the comet Swift-Tuttle. Halley's Comet causes the Orionid shower in October.
Comets are easily distinguished from asteroids by the presence of the comet tail, also known as a coma. However, very old comets may have lost all of their volatile materials that cause a coma and may eventually resemble asteroids. Asteroids are suspected to form in the inner Solar System, rather than the outer Solar system.
As of June 2008 there were 3475 known comets reported. Several hundred of these comets appear to be short period comets. However, the number of comets appear to be steadily increasing. This number does represent a small amount of the total potential comet population.
