by Ann Marie Dwyer

Created on: March 22, 2007   Last Updated: October 18, 2008

Have you ever wished upon a falling star? You have seen a meteor.

"Meteor" is the scientific name for the flash of light in the sky. They appear when a meteroid enters Earth's atmosphere. The air friction causes it to glow and spreads out a "tail" of melted meteroid and gases.

Meteoroids are the smallest members of the solar system. The largest are fragments from asteroids (pebble-sized) or comets (dust balls) and the smallest are micrometeoroids (size of a grain of sand).

They travel around the Sun in the same way that the Earth does. Each has an orbit and travels up to 26 miles per second.

When the orbit of the meteroid intersects the Earth's orbit, the meteroid enters Earth's atmosphere. Since the Earth travels at 18 miles per second, some meteors move as fast as 160,000 miles per hour. A meteroid travels across the sky as a meteor, burning up as it travels.

If remnants of the meteoroid reach Earth's surface before being totally consumed, the pieces are called meteorites. Of the 4,684 meteorites recorded, more than 1,100 have fallen in the United States. Of those, more than 1,000 were located. Libya is the country with the next largest number of recorded meteorites with 833. All of those have been found.

Meteorites are made of dense materials which cannot be consumed in flight through the Earth's atmosphere. Chondrites are the most common meteorite material and nickel/iron are the next.

Chondrules, or liquid mineral drops which solidified in low enough gravity to harden in spherical shapes, make up chondrites. These are the basic building blocks of planets and asteroids. Had they formed in high gravity, much like on the surface of the Earth, they would have formed sedimentary rocks like the mineral deposits found in the American west and the former Soviet Union.

Millions of meteors occur generally between 50 and 75 miles (80-120 km) above the Earth in the thermosphere. Though normally no more than a few feet wide, meteors are usually miles long.

Most meteors are not visible because they occur between the sun and the Earth, making them impossible to see with the naked eye.

Visible meteors are the "falling stars" or "shooting stars" that occur between the Earth and the moon. In contrast to the dark of the sky, large meteors can be seen without a telescope. Because of their speed and height, meteors are only visible for a few seconds at the longest.

Meteor showers are a group of meteors occurring at the same time. These meteoroids are usually the debris of an asteroid hit by another asteroid or a meteoroid. They travel together in a relatively small space and enter the Earth's atmosphere in rapid succession.

While meteor showers are beautiful to watch, the unstable nature of the material of the meteoroid makes it unlikely that a meteorite will fall from the sky. So, make a wish!

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