A comet is a ball of dust, ice and rock that orbits the Sun. When a comet nears the sun, it begins to boil stream out, making a long tail of dust and gas. The other part of the comet is a round, solid part called the nucleus. There are thousands of comets orbiting the Sun and they are usually named after the astronomer that discovered them.

Comets do not give off any light of their own, so we can only see them when they travel near the Sun. As comets orbit away from the heat of the Sun, they cool down. Then, the tail shrinks and leaves a path of dust behind it.

One of the most famous comets is called Halley's comet. It orbits the Earth every 76 years.