NASA - National Aeronautics and Space Administration

Meteors are bright streaks of light that appear for a very short time in the sky. They are often called shooting stars or falling stars, because they look like stars falling from the sky. The brightest meteors are sometimes called fireballs.

Image to left: A meteor appears in the sky whenever a meteoroid hurtles from space into Earth's atmosphere. Credit: World Book illustration by Rob Wood

A meteor appears when a meteoroid -- a piece of hard material -- enters the Earth's atmosphere from outer space. The Earth's atmosphere is all of the air that surrounds our planet. Air rubs against the meteoroid and heats it. This makes it glow. Most meteors glow for only about a second before they leave a shining trail.

Meteoroids usually break up into tiny pieces before reaching the Earth. Meteoroids that reach the Earth are called meteorites. Meteorites reach the Earth because they are the right size to travel through the atmosphere. If they are too small, they break up. If they are too big, they may explode. Most meteorites are quite small, about the size of a pebble.

Millions of meteors enter the Earth's atmosphere every day. At certain times every year, the Earth meets a number of clusters of tiny meteoroids. At such times, the sky seems to be filled with a shower of sparks. This is called a meteor shower.

Some meteorites are pieces of the same material that formed the planets. Scientists study meteorites for clues to the kinds of material that formed the planets.

How to cite this article: To cite this article, World Book recommends the following format: "Meteor." The World Book Student Discovery Encyclopedia. Chicago: World Book, Inc., 2005.

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