Commonly known as shooting or falling stars, meteors -- the bright streaks that dart across the night sky -- have nothing to do with stars at all. In fact, these trails of light are caused by pieces of interplanetary debris crashing into Earth's atmosphere. When a meteoroid -- a fragment of space rock -- enters Earth's atmosphere at speeds up to 70 km/s, the surrounding gas molecules energize, causing the air to glow. The bright flash that is produced by the speeding debris is called a meteor.

Some meteoroids are large enough to survive the intense heat caused by their interaction with Earth's atmosphere. Any piece of space rock that lands on the ground is called a meteorite. However, most of the particles that produce meteors are about the size of a grain of sand and never make it to Earth's surface. Every day, millions of tiny dust particles enter into the atmosphere and vaporize before anyone has a chance to see them.

Still, on any given night, it is possible to see a few meteors per hour. And, at certain times of the year, there are meteor showers with rates of 10-100 meteors per hour. Though meteor showers have nothing to do with stars, they are named for the constellations from which the meteoroids appear to fall. For example, during the Leonid meteor shower occurring in mid-November of each year, the meteors streak from the direction of the constellation Leo.

Why do these meteor showers fall during predictable periods each year? The majority of meteor showers are a result of debris left behind by comets, although some are caused by the debris of asteroids. Comets and asteroids -- rocky remnants from the formation of the solar system -- orbit distinct regions of the solar system, leaving debris in their wake. Asteroids are mostly found in the asteroid belt between the orbits of Mars and Jupiter. Comets are primarily found beyond the orbit of Neptune in the Kuiper belt or in the expansive Oort cloud. When Earth annually crosses the orbits of one of these small objects, the debris rains into our atmosphere, causing a yearly meteor shower.

Print Background Essay