What is a comet?

Comets are often described as "dirty snowballs". The solid center, or nucleus, of a comet consists mostly of ice mixed with sooty material. The nucleus is quite small and is usually only a few kilometers across

Comets travel around the Sun in an elongated orbit. They plunged out into deep space beyond the farthest planet before diving back into the solar system and passing close to the Sun. As the comet's nucleus comes closer to the Sun, it becomes smaller and may eventually break up into small fragments. Comets are thought to be as old as the solar system itself.

You can not see the nucleus of a comet with the naked eye, but you can sometimes see its tail. It appears as a smear of light that moves very gradually across the sky. As a comet moves closer to the Sun, the ice and other frozen gases in its nucleus begin to boil off, producing a long tail of gas and dust. The tail always point away from the Sun because light and other forms of radiation from the Sun push against the minute particles that are present within the tail.