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A meteoroid is a sand to boulder-sized particle of debris in the Solar System. The visible path of a meteoroid that enters Earth's (or another body's) atmosphere is called a meteor. If a meteoroid reaches the ground, it is then called a meteorite. Many meteors are part of a meteor shower. The root word meteor comes from the Greek meteōros, meaning "high in the air". It is also commonlyalthough erroneously called as a shooting star. Meteoroid (or a meteor when pass the atmosphere) is a part of a comet that explode a long time ago. When meteors enter the Earth’s atmosphere, friction makes them white-hot, causing them to appear large in the dark sky.
A small rocky or metallic object in orbit around the Sun (or another star). A meteoroid which strikes the Earth (or other largebody) is called a meteorite. As a meteoroid encounters the Earth's atmosphere frictional heating begins at an altitude of 100 to 120 km. What happens next depends on the speed, mass, and friability (tendency to break up) of the meteoroid. Micrometeoroids radiate heat so effectively that they survive unchanged to reach the surface as micrometeorites. Objects about the size of sugar grains burn up asmeteors or "shooting stars". Friable meteoroids break up and are destroyed at altitudes of 80 to 90 km. Those which are tougher survive longer and produce fireballs as their surface is melted and eaten away at temperatures of several thousand degrees. If they avoid destruction high up, they enter the lower, denser part of the atmosphere where they are rapidly decelerated. Finally, at subsonicspeeds the fireball is extinguished and the residue falls to the ground as a meteorite. The last melted material on the surface of the object solidifies to form a thin, usually black, rind known as a fusion crust.
The official definition of a meteoroid from the International Astronomical Union is "a solid object moving in interplanetary space, of a size considerably smaller than anasteroid and considerably larger than an atom” that follows an orbit. The Royal Astronomical Society has proposed a new definition where a meteoroid is between 100 µm and 10 m across. The definition includes larger objects, up to 50 m in diameter, in this category. Very small meteoroids are known as micrometeoroids (see also interplanetary dust).
The composition of meteoroids can be determined as theypass through Earth's atmosphere from their trajectories and the light spectra of the resulting meteor. Their effects on radio signals also yield information, especially useful for daytime meteors which are otherwise very difficult to observe. From these trajectory measurements, meteoroids have been found to have many different orbits, some clustering in streams (see Meteor showers) oftenassociated with a parent comet, others apparently sporadic. Debris from meteoroid streams may eventually be scattered into other orbits. The light spectra, combined with trajectory and light curve measurements, have yielded various compositions and densities, ranging from fragile snowball-like objects with density about a quarter that of ice, to nickel-iron rich dense rocks. A cluster of meteors each yearin a certain part of the sky (meteor shower).
Meteoroids travel around the sun in a variety of orbits and at various velocities. The fastest ones move at about 26 miles per second (42 kilometers per second) through space in the vicinity of Earth's orbit. The earth travels at about 18 miles per second (29 kilometers per second). Thus, when meteoroids meet the Earth's atmosphere head-on (whichwould only occur if the meteor were in a retrograde orbit), the combined speed may reach about 44 miles per second (71 kilometers per second).
See also Hydrometeor.

A meteor is the visible streak of light that occurs when a meteoroid enters the Earth's atmosphere. Meteors typically occur in the mesosphere, and most range in altitude from 75 km to 100 km. Millions of meteors occur in...
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