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Encyclopedia > Meteor
Photo of a burst of meteors with extended exposure time
Photo of a burst of meteors with extended exposure time

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. Download high resolution version (1422x1422, 393 KB) Wikipedia does not have an article with this exact name. ... Download high resolution version (1422x1422, 393 KB) Wikipedia does not have an article with this exact name. ... The shutter speed dial of a Fujika STX-1. ... Look up meteoroid in Wiktionary, the free dictionary. ... Earth (IPA: , often referred to as the Earth, Terra, the World or Planet Earth) is the third planet in the solar system in terms of distance from the Sun, and the fifth largest. ... Layers of Atmosphere (NOAA) Air redirects here. ...

Contents

Meteors in history

Meteorites have been instrumental in shaping the surface of the Earth, the moon and numerous other planets and heavenly bodies. The "man on the moon" that is often observed in Earth's lone satellite is the result of countless meteorite collisions throughout history. The moon itself is thought to have formed from debris ejected from the Earth when an asteroid or substantial series of meteorites collided with the planet.

Resulting crater from a meteorite impact
Resulting crater from a meteorite impact

Meteorites are also widely credited with the extinction of the dinosaurs and other prehistoric creatures. Image File history File links Download high-resolution version (1036x629, 106 KB) Meteor Crater, Arizona. ... Image File history File links Download high-resolution version (1036x629, 106 KB) Meteor Crater, Arizona. ...


Definitions

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. In physics, ram pressure is pressure exerted on a body which is moving at supersonic velocity through a fluid medium. ... Friction is the force that opposes the relative motion or tendency of such motion of two surfaces in contact. ... Atmospheric entry is the transition from the vacuum of space to the atmosphere of any planet or other celestial body. ...


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. The term bolide (from the Greek βολις, bolis, missile) can refer to either an extraterrestrial body that collides with the Earth, or to an exceptionally bright, fireball-like meteor regardless of whether it ultimately impacts the surface. ...


A meteor is a meteoroid that has entered the earth's atmosphere. It will then become brightly visible due to the heat produced by the ram pressure. If a meteor survives its transit of the atmosphere to come to rest on the Earth's surface, the resulting object is called a meteorite. A meteor striking the Earth or other object may produce an impact crater. Look up meteoroid in Wiktionary, the free dictionary. ... In physics, ram pressure is pressure exerted on a body which is moving at supersonic velocity through a fluid medium. ... Willamette Meteorite A meteorite is a natural object originating in outer space that survives an impact with the Earths surface without being destroyed. ... Tycho crater on Earths moon. ...


Molten terrestrial material "splashed" from such a crater can cool and solidify into an object known as a tektite. A tektite Tektites (from Greek tektos, molten) are natural glass objects, up to a few centimeters in size, which — according to most scientists — have been formed by the impact of large meteorites on Earths surface, although a few researchers favor an origin from the Moon as volcanic ejecta. ...


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.


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 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. Earths atmosphere is the layer of gases surrounding the planet Earth and retained by the Earths gravity. ... ... Patterns in the sand Sand is an example of a class of materials called granular matter. ...


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.[citation needed] In radio terminology, a receiver is an electronic circuit that receives a radio signal from an antenna and decodes the signal for use as sound, pictures, navigational-position information, etc. ... Antenna tower of Crystal Palace transmitter, London A transmitter (sometimes abbreviated XMTR) is an electronic device which with the aid of an antenna propagates an electromagnetic signal such as radio, television, or other telecommunications. ... In telecommunications and electronics, baud (pronounced , unit symbol Bd) is a measure of the symbol rate, that is the number of distinct symbolic changes (signalling event) made to the transmission medium per second in a digitally modulated signal. ...


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. Ham radio station with separate transmitter, receiver and power supply. ... Meteor scatter is a radio propagation mode that allows communications over distances of up to 1400 miles. ... Very high frequency (VHF) is the radio frequency range from 30 MHz (wavelength 10 m) to 300 MHz (wavelength 1 m). ... The Sierra Nevada is a mountain range that is almost entirely in the eastern portion of the U.S. state of California. ... Radioactive decay is the set of various processes by which unstable atomic nuclei emit subatomic particles (radiation). ... The Doppler effect is the apparent change in frequency or wavelength of a wave that is perceived by an observer moving relative to the source of the waves. ...


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. The magnetosphere shields the surface of the Earth from the charged particles of the solar wind. ... The megawatt (symbol: MW) is a unit for measuring power corresponding to one million (106) watts. ... The power spectrum is a plot of the portion of a signals power (energy per unit time) falling within given frequency bins. ... An audio frequency (abbreviation: AF) is any frequency from about 20 hertz to about 20 kilohertz, which is the approximate range of sound frequencies that is audible to humans. ...


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      Results from FactBites:
     
    Leonid MAC '99 - FACTS on meters and meteor showers (0 words)
    Meteors are better known as "shooting stars": startling streaks of light that suddenly appear in the sky when a dust particle from outer space evaporates high in the Earth's atmosphere.
    For example, a Leonid meteor of magnitude +5, which is barely visible with the naked eye in a dark sky, is caused by a meteoroid of 0.5 mm in diameter and weights only 0.00006 gram.
    The color of a meteor is an indication of its composition and the excitation temperature: sodium atoms give an orange-yellow light, iron atoms a yellow light, magnesium a blue-green light, calcium atoms may add a violet hue, while silicon atoms and molecules of atmospheric nitrogen give a red light.
    The Gloster Meteor (7242 words)
    Meteor pilots were keen to test their aircraft against the Messerschmitt Me-262 jet fighter, but at least initially they had orders not to fly beyond enemy lines lest one of their aircraft be shot down and examined.
    Meteors were fired on anyway, but none were lost to "friendly fire", though there were losses due to fatal flight accidents.
    The Meteor seemed to be no match for the MiG-15, though Australian pilots protested that they might have done much better had they been trained for air-to-air combat instead of ground support, but by the end of 1951 the Meteor had been relegated to the ground-support role.
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