Sometimes comets are referred to as “dirty snowballs” or “cosmic snowballs”. This is because they are composed mostly of ice, rock, gas and dust.
Comets orbit the Sun in elliptical paths – just like the planets. The path of a comet though is far more elliptical than that of any planet.
A comet has four components: a nucleus, a coma, a dust tail and an ion tail.
Comets have a halo when they move close to the Sun. What happens is the solar radiation vaporizes the ice and gas in the comet into a halo around it. The halo is known as the comets coma.
The ion tail of a comet is the result of solar winds that blow the gas particles directly away from the Sun.
A comet’s dust tail is a trail of dust and rocky material that is left behind as it moves along its orbit path.
Comets are believed to originate in one of two regions– the theorized Oort Cloud, or the Kuiper Belt found beyond the orbit of Neptune and the dwarf planet Pluto.
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 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.
Notable comets include Comet Hale-Bopp, which was discovered in 1995 and Comet Hyakutake, discovered in 1996. There are over 3,000 currently known comets. Scientists believe that there be up to one billion comets in our solar system. A great comet is one which is bright enough to be visible from Earth without the need for a telescope. Approximately one great comet happens every ten years.