Changes

[[Image:Meteor burst.jpg|thumb|right|200px|Photo of a part of the sky during a [[meteor shower]] over an extended [[exposure time]]. The meteors may have actually occurred several seconds to several minutes apart.]]A '''meteoroid''' is a small [[sand]]- to [[boulder]]-sized particle of debris in the [[Solar system]]. The visible path of a meteoroid that enters [[Earth|Earth's]] (or another body's) [[Earth's atmosphere|atmosphere]] is a meteor, commonly called a "shooting star" or "falling star". On reaching the ground, a meteor is then called a meteorite. Many meteors are part of a [[meteor shower]]. The root word '''meteor''' comes from the [[Ancient Greek|Greek]] ''meteōros'', meaning ''high in the air''.

[[Image:IMG 8505n3.JPG|thumb|175px|A meteor (possibly 2) and [[Milky way]].]]Larger than a meteoroid, the object is an [[asteroid]]; smaller than that, it is [[interplanetary dust]]. The current official definition of a meteoroid from the [[''International Astronomical Union]] '' is "a solid object moving in interplanetary space, of a size considerably smaller than an asteroid and considerably larger than an atom."<ref>http://www.imo.net/glossary Glossary International Meteor Association</ref> The [[''Royal Astronomical Society]] '' has proposed a new definition where a meteoroid is between 100 [[Micrometre|(µm]] ) and 10 m across.<ref>{{cite journal

The composition of meteoroids can be determined as they pass through Earth's atmosphere from their trajectory 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]]) often associated with a parent [[comet]], others apparently sporadic. 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,<ref>Povenmire, H. [http://www.lpi.usra.edu/meetings/lpsc2000/pdf/1183.pdf PHYSICAL DYNAMICS OF THE UPSILON PEGASID FIREBALL – EUROPEAN NETWORK 190882A]. Florida Institute of Technology</ref> to nickel-iron rich dense rocks. A relatively small percentage of meteoroids hit the Earth's atmosphere and then pass out again: these are termed [[The Great Daylight 1972 Fireball#All known Earth-grazing fireballs|Earth-grazing fireballs]].

[[Image:Comet holmes and Geminid121307.jpg|[[Comet]] [[17P/Holmes]] and [[Geminid]].|thumb|left|200px]]

Many meteoroids are formed by impacts between asteroids though many are also left in trails behind [[comets]] that form [[meteor showers]] and many members of those trails are eventually scattered into other orbits forming random meteors too. Other sources of meteors are known to have come from impacts on the [[Moon]], or [[Mars]] as some meteorites from them have been identified. See [[Lunar meteorite]]s and [[Mars meteorite]]s.