Comets orbit the Sun in highly ______________________ orbits. Their velocity increases greatly when they are near the Sun and ______________________ down at the far reaches of the orbit. Comets are light only when they are near the Sun (when the gas is ______________________); 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 ______________________ up; these comets are called ______________________.

The ______________________ 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 ______________________. This is called a meteor shower; in it, many meteors fall through the atmosphere in a relatively short time.