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