Meteor
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The centre dot is an Asteroid being followed by the sequence; the object that flashes by near the end is a meteor. |
A
meteor is the visible path of a
meteoroid that enters the
Earth's (or another body's)
atmosphere, commonly called a
shooting star or
falling star.
For bodies with a size scale larger than the atmospheric mean free path (10 cm to several meters) the visibility is due to the heat produced by the
ram pressure (
not friction, as is commonly assumed) of
atmospheric entry. Since the majority of meteors are from small sand-grain size meteoroid bodies, most visible signatures are caused by electron relaxation following the individual collisions between vaporized meteor atoms and atmospheric constituents.
A very bright meteor may be called a fireball or
bolide. The International Meteor Organisation defines fireballs as being meteors of magnitude -3 or brighter. The meteor section of the British Astronomical Association on the other hand has a much stricter definition, requiring the meteor to be magnitude -5 or brighter.
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.
Meteor dust particles left by falling meteoroids can persist in the atmosphere for up to several months. These particles might affect climate, both by scattering electromagnetic radiation and by catalyzing chemical reactions in the upper atmosphere.
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 last up to 45 minutes 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 off 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 upon one's position with respect to the mirror. Because the sporadic nature of meteor entry, such systems are limited to low data rates, typically 459600
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 frequencies. Curiously, although the waves are electromagnetic, they can be heard: they are powerful enough to make grasses, plants, eyeglass frames, frizzy hair, the middle ear and other materials vibrate. See for example,
Listening to Leonids (NASA, 2001),
Hearing Sensations in Electric Fields (1964),
Human auditory system response to Modulated electromagnetic energy (J. Appl. Physiol. 17(4):689-692. 1962),
Human Perception of Illumination with Pulsed Ultrahigh-Frequency Electromagnetic Energy (Science 27 July 1973 Vol. 181. no. 4097, pp. 356 - 358) for details and references on the electrophonic auditory phenomenon.
At times, although not frequent, sections of what appear to be a meteor are actually pieces of a sun (distant star) that has gone supernova.
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Meteor showers - view tips
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Meteor Rock anyone? says Ebay*
Baetylus*
Impact crater*
Meteor shower*
meteoroid*
meteorite*
tektite*
bolide*
Green Fireballs
