- Comets are often referred to as "dirty snowballs" or "cosmic snowballs" due to their being composed of ice, rocks, gas, and dust.
- Like the planets, comets orbit the Sun in elliptical paths. However, a comet's orbit is far more elliptical than that of any planet.
- Comets are composed of four components: nucleus, coma, dust tail, and ion tail.
- A comet's nucleus contains the vast majority of its mass.
- As a comet moves closer to the Sun, solar radiation vaporrizes the ice and gas found in the comet into a halo around the comet. This halo is the comet's coma.
- A comet's ion tail is the result of solar winds blowing the gas particles directly away from the Sun.
- A comet's dust tail is the trail of dust and rocky material left behind along the comet's orbit.
- Comets are thought to originate in one of two theorized regions in the Solar System: the Oort Cloud of the Kuiper Belt.
- The Oort cloud is an outer region of the Solar System 50,000-150,00 times the distance from the Sun to Earth that is believed to contain dormant comets. Some of the comets that originate here have orbits lasting millions of years.
- The Kuiper Belt is ring of dormant comets located just beyond the orbit of Neptune. The comets originating here have orbits lasting hundreds of years or fewer.
- The most famous comet is Halley's Comet. It has been observed since at least 240 B.C. Its orbit makes it visible from Earth every 76 years. It was named after the British astronomer Edmond Halley.
Other notable comets are Comet Hale-Bopp, which was discovered in 1995 and Comet Hyakutake, discovered in 1996.
- Currently, there are over 3000 known comets. However, scientists predict that there could be up to one billion comets in our solar system.
Great comets are comets that are bright enough to be visible from Earth without a telescope. Approxiamtely one great comet occurs every ten years.