Shooting stars, or 'meteors', are tiny fragments of space rubbish, which usually burn up when they hit the Earth's upper atmosphere, leaving only a short bright trail of light behind them. Many meteors can be predicted - they happen in showers once a year, as the Earth crosses over the trail of dust and debris left behind by a comet. Large meteors that hit the Earth are called meteorites. They tend to be the tougher, asteroid-like material, rather than the flimsy iceballs which comets leave behind.
Meteorites fall into three main categories - irons, stones, and stony irons.
They are the most common type found on Earth - at least partly because they are most likely to survive the heat when entering the atmosphere, and also because they tend to stand out from rocks on Earth. Stone meteorites, on the other hand, are very similar to the rocks which make up the Earth's crust itself. They probably outnumber the iron meteorites, but they are not so heat resistant, and often blend in with rocks in the landscape. Stony iron meteorites are a cross between the two types. The stony types are often peppered with tiny globules of glassy material, called 'chondrules'.