Comets are made of ice and dust.In the orbit in the outer reaches of the solar system they are dark and cold, but when they approach the sun they heat up and start glowing tails if dust and gas blowing away from sun.

Comets originate at the edge of the solar system and have large elliptical orbits.Comets gas tails can reach100 million km long and always point away from sun.

“The recently discovered object, known as comet ISON, is due to fly within 1.2 million miles (1.9 million km) from the center of the sun on Nov. 28, 2013 said astronomer Donald Yeomans, head of NASA’s Near Earth Object Program at the Jet Propulsion Laboratory in Pasadena, Calif.”