A Meteor is a luminous trail in the sky produced when a meteoroid burns up in the atmosphere. It is commonly referred to as a "shooting star". Sometimes many meteoroids may hit the atmosphere around the same time, giving us a meteor shower.

So what's a Meteoroid?
This refers to the particle itself without relation to the phenomena it produces when entering the Earth's atmosphere (a meteor). A meteoroid is matter revolving around the sun or any object in interplanetary space that is too small to be called an asteroid or a comet. Even smaller particles are called micro-meteoroids or cosmic dust grains, which includes any interstellar material that should happen to enter our solar system. A meteoroid becomes a meteorite if it survives its plunge through the atmosphere and reaches the surface of the earth.

Meteorites
Most meteorites come from asteroids, including a few believed to have come specifically from 4 Vesta (one of the largest asteroids in our solar system). A few probably come from comets. Of the 10s of thousands known, a very small number of meteorites have been shown to be of Lunar (23 finds) or Martian (perhaps as many as 18) origin. The largest known meteorites are about the size of a telephone booth. But there is clear evidence that even larger objects have hit earth in the past.

Though meteorites may appear to be just boring rocks, they are extremely important in that we can analyze them carefully in our labs. Aside from the few kilos of moon rocks brought back by the Apollo and Luna missions, meteorites are our only material evidence of the universe beyond the Earth.

Composition of Meteorites
Basically, there are two kinds of meteorites: Iron (about 4.8% of meteorites found) and Stony (about 94%). Stony Meteorites being the most common, also have a bit more variety. there are three sub-classifications of stonys: Chondrites, containing chondrules, Carbonaceous Chondrites, containing chondrules along with volatile minerals and Achondrites which contain no chondroles. Then, there is a final very rare kind of mixed meteorite, referred to as Stony-Iron (about 1.2%).

Iron Meteorites
These meteorites are made of a crystalline iron-nickel alloy. Scientists believe that they resemble the outer core of the Earth.

Widmanstatten Patterns (shown to the left) are seen in iron meteorites. This pattern is made up of two metals. These two alloys of Nickel and Iron crystalize at slightly different temperatures. So slightly that the cooling rate has to be about 1 degree per million years in order for this pattern to emerge. This could only happen in the molten core of a planet, and serves as proof that these objects could not have come from the earth.