Photo courtesy of NASA

by Brad Bell and Kyle Butler

Meteors are small bodies in space, pieces of stony or metallic fragments smaller than asteroids; most of them are as small as a pebble. The brightest of the meteors are called fireballs, because when they begin to fall to the Earth, they burn up in the atmosphere, creating a shining trail of gases and melted meteor particles, a streak of light in the sky. The gases include vaporized material and atmospheric gases that heat up when a meteor passes through the Earth's atmosphere. Friction between the meteors and the atmosphere causes them to heat up to the point that they glow and become visible to us on most dark nights. If you have seen one, that is why it appears to be red with smoke trailing behind it. Most meteors glow for only a few seconds before burning up; some people call them falling or shooting stars. They leave a trail that lasts several minutes. Meteors become visible about 65 to 120 km above the Earth. They meet the Earth's atmosphere head on. The combined speed of the meteor and the Earth's gravitational force may reach about 42 km per second. Meteors have done minor damage to spacecrafts; about 100 tiny craters and chipped areas have been found on the Hubble Space Telescope, caused by tiny meteors.

At certain times of the year, meteor showers happen occasionally when the Earth passes through an orbiting stream of fragments from a comet that has broken up. They usually occur in spring and usually do not hit the ground. Some meteors sound like thunder; sonic booms often follow the appearance of meteors, and the sky seems filled with a shower of sparks. Meteor showers occur on about the same dates each year. The most brilliant meteor showers known took place on November 12-13, 1833; it was one of the Leonid showers, which occur every November and seem to come from the direction of the constellation Leo.

If a meteor breaks through the Earth's atmosphere, does not burn up completely, and hits the Earth's surface, it is called a meteorite. Over 100 meteorites hit the Earth each year; fortunately, most are very small. The larger meteorites come from the asteroids in the Asteroid Belt. Some of the smaller meteorites are moon rocks, while others are pieces of Mars. The Hoba iron meteorite is the largest meteorite known; its weight is about 66 tons. It has never been moved from its landing site in Namibia, Africa.

Bibliography and Additional Sources of Information

Comets and Meteor Showers

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