Comets orbit the Sun in highly elliptical orbits. Their velocity increases greatly when they are near the Sun and slows down at the far reaches of the orbit. Comets are light only when they are near the Sun (when the gas is vaporizing); comets are dark (virtually invisible) throughout most of their orbit. We can only see comets when they're near the Sun. Some comets crash into the Sun or get so close that they burn up; these comets are called sungrazers.

The Earth passes through the orbit of some comets. When this happens, the left-over comet comet debris (rocks, etc.) bombards the Earth, and the debris burns up in our atmosphere. This is called a meteor shower; in it, many meteors fall through the atmosphere in a relatively short time.

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