Comets are pieces of rocky ice orbiting around the Sun. Their orbits take them close to the Sun, but also very far from it, often beyond our Solar System.
Comets are invisible until they come near the Sun. When they do, the Sun melts some of their ice. This ice turns into gases and dust, creating a long glowing tail behind the comet. This tail of dust and gas can stretch to millions of kilometers into space, always pointing away from the Sun.
Scientists believe that comets form in the colder part of our Solar system, far beyond the orbit of planet Pluto.
Comets travel alone. The most famous comet of all is Haley’s comet. Haley’s comet is a long-period comet; it appears once every 76 years. The last time was in 1986; it will appear again in 2062.
To travel around the Sun, some comets need less time than Haley’s comet. They are known as the short-period comets. The very long-period comets need thousands of years, and some pass the Sun once and never return.
Many scientists believe that the dinosaurs died, when a comet crashed into Earth. The crash made big clouds of gas and dust around the Earth. With no sunlight, plants could not grow and dinosaurs had no food.
© 2005 Al Bawaba (www.albawaba.com)
