Rocks That Fly

HAVE you ever seen a shooting star blaze across the sky on a clear night? It may be just a matter of time before you do. According to scientists these fireworks of nature trace their paths across earth’s skies some 200,000,000 times every day!

What are they? They are simply chunks of stony or metallic matter known as meteoroids that light up in white heat as they enter the earth’s atmosphere. The bright streak of light they trace across the sky as observed from earth is known as a meteor.

Most meteoroids burn up completely before they reach the earth, but some survive the intense heat and reach the earth’s surface. These are known as meteorites. Some scientists estimate that each day some 1,000 tons of this flying rock is deposited on earth.a

These crashes are seldom dangerous to humans, mainly because of the relatively small size of these flying rocks. In fact, most meteors are caused by meteorites no larger than a grain of sand. (See box, “Rocks From Outer Space.”)

Meteoroid: A relatively small chunk of metallic or stony matter floating in space or falling through the atmosphere. Some scientists think that most meteoroids are fragments from asteroids produced by collisions or by the rocky debris from extinct comets.

Meteor: When a meteoroid penetrates the earth’s atmosphere, the air friction produces intense heat and a bright glow. This trail of hot glowing gases is momentarily visible as a streak of light in the sky. The streak of light is known as a meteor. Many call it a shooting star or a falling star. Most meteors are first sighted when they are about 65 miles [100 km] above the earth’s surface.

Meteorite: Sometimes a meteoroid is so large that it does not burn up completely when entering our atmosphere, and it crashes into the earth. Meteorite is the term for such a meteoroid. Some can be very large and heavy. One meteorite in Namibia, Africa, weighs more than 60 tons. Other large meteorites weighing 15 tons or more have been found in Greenland, Mexico, and the United States.