Meteoroid

Meteoroid - Wikipedia, the free encyclopedia
A meteoroid is a small sand- to boulder-sized particle of debris in the Solar system. ... On the Definition of the Term Meteoroid" ...
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meteoroid: Definition from Answers.com
meteoroid ( ) n. A solid body, moving in space, that is smaller than an asteroid and at least as large as a speck of ... On the Definition of the Term Meteoroid" ...
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Veropedia - Meteoroid
A meteoroid is a small sand to boulder-sized particle of debris in the Solar system. ... On the Definition of the Term Meteoroid" ...
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StarChild: Meteoroids
A meteoroid is a piece of stony or metallic debris which travels in outer space. Meteoroids travel around the Sun in a variety of orbits and at various speeds. ...
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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 (or another body's) Earth's atmosphere is a meteor, commonly called a "shooting star" or "falling star". Many meteors are part of a meteor shower.

Definitions The root word meteor comes from the Ancient Greek meteōros, meaning high in the air.

Meteoroid A meteoroid is a small sand to boulder-sized particle of debris in the Solar system. Larger than that, 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 or molecule." The Royal Astronomical Society has proposed a new definition where a meteroid is between 100 Micrometre and 10 m across.)The near-earth object definition includes larger objects, up to 50 m in diameter, to this category.

Meteor A meteor is the visible event that occurs when a meteoroid or asteroid enters Earth's atmosphere and becomes brightly visible. For bodies with a size scale larger than the atmospheric mean free path (10 cm to several metres) 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. The meteor is just what we see.

Fireball A fireball is a very bright meteor. The International Astronomical Union defines a fireball as "a meteor brighter than any of the planets" (Apparent magnitude -4 or greater). MeteorObs Explanations and Definitions (states IAU definition of a fireball) The International Meteor Organization (an amateur organization that studies meteors) has a more rigid definition. It defines a fireball as a meteor that would have a magnitude of -3 or brighter if seen at zenith. This definition corrects for the greater distance between an observer and a meteor near the horizon. For example, a meteor of magnitude -1 at 5 degrees above the horizon would be classified as a fireball because if the observer had been directly below the meteor it would have appeared as magnitude -6. International Meteor Organization - Fireball Observations

===Bolide===The word bolide comes from the Greek language βολις, (bolis) which can mean a missile or to flash. The IAU has no official definition of bolide and generally considers the term synonymous with fireball. The term is more often used among geologists than astronomers where it means a very large impactor. For example, the United States Geological Survey uses the term to mean a generic large crater forming projectile "to imply that we do not know the precise nature of the impacting body . . . whether it is a rocky or metallic asteroid, or an icy comet, for example". usgs.gov - What is a Bolide? Astronomers tend to use the term to mean an exceptionally bright fireball, particularly one that explodes (sometimes called a detonating fireball).

Meteorite A meteorite is a portion of a meteoroid or asteroid that survives its passage through the atmosphere and impact with the ground without being destroyed. Meteorites are sometimes, but not always, found in association with hypervelocity impact craters; during energetic collisions, the entire impactor may be vaporized, leaving no meteorites.

Tektite Molten terrestrial material "splashed" from a crater can cool and solidify into an object known as a tektite. These are often mistaken for meteorites.

Meteoric dust Most meteoroids are destroyed when they enter the atmosphere. The left-over debris is called meteoric dust or just meteor dust. Meteor dust particles 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 or asteroid into the upper atmosphere, an ionization trail is created, where the molecules in the upper atmosphere are ionization 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 burst communications.

Meteor radars can measure atmospheric density and winds by measuring the decay rate and Doppler shift of a meteor trail.

Sound Numerous people have over the years reported sounds being heard while bright meteors flared overhead. This would seem impossible, given the relatively slow speed of sound. Any sound generated by a meteor in the upper atmosphere, such as a sonic boom, should not be heard until many seconds after the meteor disappeared. However, in certain instances, for example during the Leonid meteor shower of 2001, several people reported sounds described as "crackling", "swishing", or "hissing"http://findarticles.com/p/articles/mi_m1134/is_6_111/ai_87854873/pg_1 occurring at the same instant as a meteor flare. Similar sounds have also been reported during intense displays of Earth's Aurora (astronomy).

Many investigators believe the sounds to be imaginary... essentially sound effects added by the mind to go along with a light show. However, the persistence and consistency of the reports have caused others to wonder. And sound recordings made under controlled conditions in Mongolia in 1998 by a team lead by Slaven Garaj, a physicist at the École Polytechnique Fédérale de Lausanne, supports the contention that the sounds are real.

How these sounds could be generated, assuming they are in fact real, remains something of a mystery. It has been hypothesized that the turbulent ionized wake of a meteor interacts with the magnetic field of the Earth, generating pulses of radio waves. As the trail dissipates, megawatts of electromagnetic energy could be released, with a peak in the power spectrum at audio frequency. Physical vibrations induced by the electromagnetic impulses would then be heard if they are powerful enough to make grasses, plants, eyeglass frames, and other conductive materials vibrate. Listening to Leonids Hearing Sensations in Electric Fields Human auditory system response to Modulated electromagnetic energy. Human Perception of Illumination with Pulsed Ultrahigh-Frequency Electromagnetic Energy This proposed mechanism, although proven to be plausible by laboratory work, remains unsupported by corresponding measurements in the field.

Formation 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 meteorites and Mars meteorites.

Orbit Meteoroids and asteroids orbit around the Sun. Not all of the orbits are the same. Some of these objects orbit together (stream component); these are probably comet remnants that would form a meteor shower. Other meteors are not associated with any clustering of meteoroids to form a shower (though there must also be meteoroids clustered in orbits which do not intercept Earth's or any other planet). The fastest objects travel at roughly 26 miles per second (42 km per second) through space in the vicinity of Earth's orbit. Together with Earth's orbital motion of 18 miles per second (29 km per second) speeds can reach 44 miles per second (71 kilometers per second) in head-on collisions. This means the meteor would also be in a retrograde orbit and have roughly a fifty percent chance of a daylight (or near daylight) event as Earth orbits in the direction of roughly west at noon. Most meteors are observed at night as light conditions allow fainter observations but meteors are still seen from 40 to 75 miles away high in the sky above observers. NASA Home > World Book @ NASA, Meteors

A number of specific meteors have been observed, largely by members of the public and largely by accident, but with enough detail that orbits of the incoming meteors or meteorites have been calculated. All of them came from orbits from the vicinity of the Asteroid Belt. Diagram 2: the orbit of the Peekskill meteorite along with the orbits derived for several other meteorite falls

Perhaps the best-known meteor/meteorite fall is the Peekskill Meteorite which was filmed on October 9, 1992 by at least 16 independent videographers. The Peekskill Meteorite October 9, 1992 Videos]

Eyewitness accounts indicate that the fireball entry of the Peekskill meteorite started over West Virginia at 23:48 UT (+/- 1 min.). The fireball, which traveled in a northeasterly direction had a pronounced greenish colour, and attained an estimated peak visual magnitude of -13. During a luminous flight time that exceeded 40 seconds the fireball covered a ground path of some 700 to 800 km.

One meteorite recovered at Peekskill, N.Y., for which the event and object gained its name, (at 41.28 deg. N, 81.92 deg. W) had a mass of 12.4 kg and was subsequently identified as an H6 monomict breccia meteorite."Meteoritical Bull", by Wlotzka, F. published in "Meteoritics", # 75, 28, (5), 692, 1994. The video record suggests that the Peekskill meteorite probably had several companions over a wide area especially in the harsh terrain in the vicinity of Peekskill.

Spacecraft damage Even very small meteoroids can damage spacecraft. The Hubble Space Telescope for example, has about 572 tiny craters and chipped areas.http://www.space.com/scienceastronomy/astronomy/hubble_impact_020226.html

See also

Baetylus
Impact crater
Meteor shower
Meteorite
Tektite

References External links

Meteoroids Page at NASA's Solar System Exploration
International Meteor Organization fireball page
British Astronomical Society fireball page
A Goddard Space Flight Center Science Question of the Week where the answer mentions that a fireball will cast a shadow.
Meteor showers - view tips
Meteor shower predictions
Society for Popular Astronomy - Meteor Section

Meteoroid - Wikipedia, the free encyclopedia
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's (or another body's) atmosphere is a meteor ...

Definition: meteoroid from Online Medical Dictionary
The Online Medical Dictionary is a searchable dictionary of definitions from medicine, science and technology.

AskOxford: meteoroid
meteoroid • noun a small body that would become a meteor if it entered the earth’s atmosphere. Perform another search of the Compact Oxford English Dictionary

meteoroid - Wiktionary
Definition from Wiktionary, a free dictionary

meteoroid definition of meteoroid in the Free Online Encyclopedia.
meteoroid: see meteor meteor, appearance of a small particle flying through space that interacts with the earth's upper atmosphere. While still outside the atmosphere, the particle ...

meteoroid - Hutchinson encyclopedia article about meteoroid
Small natural object in interplanetary space. Meteoroids are smaller than asteroids, ranging from the size of a pebble up, and move through space at high speeds.

meteoroid - definition of meteoroid by the Free Online Dictionary ...
me·te·or·oid (m t--roid) n. A solid body, moving in space, that is smaller than an asteroid and at least as large as a speck of dust. meteoroid

meteoroid definition |Dictionary.com
noun Astronomy. any of the small bodies, often remnants of comets, traveling through space: when such a body enters the earth's atmosphere it is heated to luminosity and becomes a ...

Meteoroids: Zoom Astronomy
Meteoroid Orbits Meteoroids orbit around the Sun; different meteoroids travels at different speeds and in different orbits. Some meteoroids orbit together (called stream component ...

meteoroid: Definition from Answers.com
meteoroid ( ) n. A solid body, moving in space, that is smaller than an asteroid and at least as large as a speck of