The light is caused by a small speck of dust burning when it enters the earth's atmosphere. The dust comes from comets. These pieces of comet dust are called meteoroids. Most meteoroids are smaller than a grain of sand. The flash of light is called a meteor.
Meteors usually last just a second or two.
Sometimes, there are meteor showers. In a meteor shower, lots of shooting stars seem to fall from one area of the sky. These meteor showers happen when the Earth travels through a stream of dust following a comet. Some people get comets and meteors mixed up. A comet is very different from a meteor.