Spark image

Comet are huge balls of grit and ice many kilometers in diameter.

When they come near the Sun the heat melts some of the ice and this produces a huge cloud of gas and dust that we see as the tail of the comet. These tails, millions of kilometers in length, become visible as they near the Sun. The tail always points away from the Sun because of the pressure of the solar wind on its tiny particles.

We only see a comet for a short time because they move fast when they are close to the Sun but very slowly in the outer parts of their orbit, see Keplerís second law. Comets are thought to originate in the Oort cloud, about 40 000 AU from the Sun and in the Kuiper belt.

© Keith Gibbs 2009