The cycles of the Sun, Moon and Stars are very regular, and we know where they will be for hundreds of years. Not everything in space is like that, though. The bright tail of a comet and the streak of a meteor are two of the most beautiful surprises in nature. Very large chunks of rock in space are called asteroids. Thousands of asteroids orbit between Mars and Jupiter in the Asteroid belt.
Meteoroids are smaller chunks of rock in space.
When they enter our atmosphere they start to burn, and are called meteors. Meteors streak across the sky, blazing bright for only a few seconds. As the Earth moves in its orbit around the Sun, it occasionally crosses the stream of dust left by a comet, and this causes a meteor shower. Sometimes meteors are large enough to survive the fiery trip through the atmosphere, and actually hit the ground. These are called meteorites.