[h=1]Meteoroid[/h]A meteoroid is a small rocky or metallic body travelling through space. Meteoroids are significantly smaller than asteroids, and range in size from small grains to 1 meter-wide objects. Smaller objects than this are classified as micrometeoroids or space dust. Most are fragments from comets or asteroids, while others are collision impact debris ejected from bodies such as the Moon or Mars.
When such an object enters the Earth's atmosphere, it heats up from atmospheric friction and produces a streak of light, both from the glowing object and the trail of glowing particles that it leaves in its wake. This phenomenon is called a meteor, or colloquially a "shooting star" or "falling star". A series of many meteors appearing seconds or minutes apart, and appearing to originate from the same fixed point in the sky, is called a meteor shower. Incoming objects larger than several meters (asteroids or comets) can explode in the air. If a meteoroid, comet or asteroid or a piece thereof withstands ablation from its atmospheric entry and impacts with the ground, then it is called a meteorite.
Around 15,000 tonnes of meteoroids, micrometeoroids and different forms of space dust enter Earth's atmosphere each year.
[h=2]Meteor[/h]A meteor or "shooting star" is the visible streak of light from a meteoroid or micrometeoroid, heated and glowing from entering the Earth's atmosphere, as it sheds glowing material in its wake. Meteors typically occur in the mesosphere at altitudes between 76 to 100 km (47 to 62 mi). The root word meteor comes from the Greek meteōros, meaning "suspended in the air".
Millions of meteors occur in the Earth's atmosphere daily. Most meteoroids that cause meteors are about the size of a pebble. Meteors may occur in showers, which arise when the Earth passes through a stream of debris left by a comet, or as "random" or "sporadic" meteors, not associated with a specific stream of space debris. A number of specific meteors have been observed, largely by members of the public and largely by accident, but with enough detail that orbits of the meteoroids producing the meteors have been calculated. All of the orbits passed through the asteroid belt. The atmospheric velocities of meteors result from the movement of Earth around the Sun at about 30 km/s (18 miles/second), the orbital speeds of meteoroids, and the gravity well of Earth.
Source : Wikipedia
A Leonid meteor, seen in the 2009 Leonid Meteor Shower.
