Meteor

A meteor is the visible path of a meteoroid that enters the Earth (or another body's) Earth's atmosphere, commonly called a shooting star or falling star. The visibility is due to the heat produced by the ram pressure (not friction, as is commonly assumed) of atmospheric entry. A very bright meteor, brighter than the apparent magnitude of Venus (planet), may be called a fireball or bolide. If a meteoroid survives its transit of the atmosphere to come to rest on the surface, the resulting object is called a meteorite. A meteor striking the Earth or other object may produce an impact crater. Molten terrestrial material 'splashed' from such a crater can cool and solidify into an object known as a tektite. ==Ionization trails== During the entry of a meteoroid into the upper atmosphere, an ionization trail is created, where the molecules in the upper atmosphere are ionized by the passage of the meteor. Such ionization trails can persist up to a minute at a time. Small, sand-grain sized meteoroids are entering the atmosphere constantly, essentially every few seconds in a given region, and thus ionization trails can be found in the upper atmosphere more or less continuously. When radio waves are bounced of these trails, it is called meteor scatter communication. Meteor scatter has been used for experimental secure military battlefield communications systems. The basic idea of such a system is that such an ion trail will act as a mirror for radio waves, which can be bounced off the trail. Security arises from the fact that as a mirror, only receivers in the correct position will hear the transmitter, much as with a real mirror, what is seen in reflection depends on one's position with respect to the mirror. Because the sporadic nature of meteor entry, such systems are limited to low data rates, typically 9600 baud. Amateur radio operators sometimes use meteor scatter communication on VHF bands. Snowpack information from the Sierra Nevada mountains in California is transmitted from remote sites via meteor scatter. Meteor radars can measure atmospheric density and winds by measuring the decay rate and Doppler shift of a meteor trail. Large meteoroids can leave behind very large ionization trails, which then interact with the Earth's magnetic field. As the trail dissipates, megawatts of electromagnetic energy can be released, with a peak in the power spectrum at audio frequency. Curiously, although the waves are electromagnetic, they can be heard: they are powerful enough to make grasses, plants, eyeglass frames, frizzy hair and other materials vibrate. See for example, [http://science.nasa.gov/headlines/y2001/ast26nov_1.htm Listening to Leonids] (NASA, 2001) for details and references on the auditory phenomenon. == See also == *Impact crater *Meteor shower *meteoroid *meteorite *tektite *bolide Meteoroids th:ดาวตก vi:Sao băng

Meteor

N. Great job on the definitions. It's so rare to see these concepts presented accurately. :Concur. But, is a meteor ''the visible path''? Or is it the actual piece of rock? :As defined at the moment the subsequent sentence ''A meteor striking the Earth'' seems wrong. :Oxford and Cambridge dictionaries say it's the rock. Others say the trail. --User:Eddie Dealtry 18:59, 7 Jan 2005 (UTC) == meteor is the path == Meteor is really only the visible path, the light. The own word meteor comes from word meteo (in Greece something like atmosphere or something like that); meteorology is a science about meteors. It was believed meteor is appearence in atmosphere, like lighting or rain. --User:195.113.24.190 09:00, 10 May 2005 (UTC) "Hygro-meteors" are raindrops User:JohnElder 02:13, 13 Jun 2005 (UTC)

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