Photo of a part of the sky during a meteor shower over an extended exposure time. A meteor shower, some of which are known as a "meteor storm" or "meteor outburst" is a celestial event where a group of meteors are observed to radiate from one point In Photography, shutter speed is the length of time a shutter is 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. Sand is a naturally occurring Granular material composed of finely divided rock and Mineral particles In Geology, a boulder is a rock with grain size of usually no less than 256 mm (10 Inches diameter The Solar System consists of the Sun and those celestial objects bound to it by Gravity. The visible path of a meteoroid that enters Earth's (or another body's) atmosphere is a meteor, commonly called a "shooting star" or "falling star". EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five Many meteors are part of a meteor shower. A meteor shower, some of which are known as a "meteor storm" or "meteor outburst" is a celestial event where a group of meteors are observed to radiate from one point The root word meteor comes from the Greek meteōros, meaning high in the air. The Ancient Greek language is the historical stage in the development of the Hellenic language family spanning the Archaic (c

Meteoroid

A meteor (possibly 2) and Milky way

Larger than a meteoroid, the object is an asteroid; smaller than that, it is interplanetary dust. The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply Asteroids, sometimes called Minor planets or planetoids', are bodies—primarily of the inner Solar System —that are smaller than planets but 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. "^[1] The Royal Astronomical Society has proposed a new definition where a meteoroid is between 100 µm and 10 m across. The Royal Astronomical Society (RAS is a Learned society that began as the Astronomical Society of London in 1820 to support astronomical research A micrometre ( American spelling: micrometer; symbol µm) is one millionth of a Metre, or equivalently one thousandth of a Millimetre ^[2] The NEO definition includes larger objects, up to 50 m in diameter, to this category. Near-Earth objects ( NEOs) are Asteroids Comets and large Meteoroids whose orbits bring them close ( Perihelion distance AU

Meteor

Comet 17P/Holmes and Geminid

A meteor is the visible event that occurs when a meteoroid or asteroid enters Earth's atmosphere and becomes brightly visible. A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail — 17P/Holmes is a Periodic comet in our Solar system, discovered by the British amateur astronomer Edwin Holmes on November 6, 1892. The Geminids are a Meteor shower caused by an object named 3200 Phaethon, which is thought to be an extinct Comet. Asteroids, sometimes called Minor planets or planetoids', are bodies—primarily of the inner Solar System —that are smaller than planets but 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. In Physics the mean free path of a particle is the average distance covered by a particle ( Photon, Atom or Molecule) between subsequent impacts In Physics, ram pressure is a pressure exerted on a body which is moving through a Fluid medium Friction is the Force resisting the relative motion of two Surfaces in contact or a surface in contact with a fluid (e 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 simply the visible event rather than an object itself.

Fireball

A fireball is brighter than a usual meteor. The International Astronomical Union defines a fireball as "a meteor brighter than any of the planets" (magnitude -4 or greater). The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value ^[3] The International Meteor Organization (an amateur organization that studies meteors) has a more rigid definition. The International Meteor Organization (IMO was founded in 1988 and has several hundred members It defines a fireball as a meteor that would have a magnitude of -3 or brighter if seen at zenith. In broad terms the zenith is the direction pointing directly above a particular location ( Perpendicular, Orthogonal) 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. ^[4]

Bolide

The word bolide comes from the Greek βολις, (bolis) which can mean a missile or to flash. Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly 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. A geologist is a contributor to the Science of Geology, studying the physical structure and processes of the Earth and planets of the solar system Historically Astronomy was more concerned with the classification and description of phenomena in the sky while Astrophysics attempted to explain these phenomena For example, the USGS 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 . The United States Geological Survey ( USGS) is a scientific agency of the United States government. . . whether it is a rocky or metallic asteroid, or an icy comet, for example". ^[5] 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. A meteorite is a natural object originating in Outer space that survives an impact with the Earth 's surface 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. In the broadest sense the term impact crater can be applied to any depression natural or manmade resulting from the high velocity impact of a projectile with larger body

Tektite

Two tektites

Molten terrestrial material "splashed" from a crater can cool and solidify into an object known as a tektite. Tektites (from Greek tektos, molten are natural Glass objects up to a few centimeters in size which most scientists argue were formed by the impact of 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 ionized by the passage of the meteor. Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five Ionization is the physical process of converting an Atom or Molecule into an Ion by adding or removing charged particles such as Electrons 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. Sand is a naturally occurring Granular material composed of finely divided rock and Mineral particles When radio waves are bounced off these trails, it is called meteor burst communications. Meteor burst communications, or MBC for short is a radio Propagation mode that exploits the ionized trails of Meteors during Atmospheric

Meteor radars can measure atmospheric density and winds by measuring the decay rate and Doppler shift of a meteor trail. Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. The Doppler effect (or Doppler shift) named after Christian Doppler, is the change in Frequency and Wavelength of a Wave for

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"^[6] occurring at the same instant as a meteor flare. For a list of famous people named Leonid please see Leonid (a disambiguation page Similar sounds have also been reported during intense displays of Earth's auroras.

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 Swiss Federal Institute of Technology at Lausanne, support the contention that the sounds are real. Lausanne ( pronounced, Losanna is a city in Romandy, the French -speaking part of Switzerland, situated on the shores of Lake Geneva

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 frequencies. The watt (symbol W) is the SI derived unit of power, equal to one Joule of energy per Second. In Statistical signal processing and Physics, the spectral density, power spectral density ( PSD) or energy spectral density ( An audio frequency (abbreviation AF) or audible frequency is characterized as a periodic vibration whose Frequency is audible to the average human 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. ^{[7][8][9][10]} 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. A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail — A meteor shower, some of which are known as a "meteor storm" or "meteor outburst" is a celestial event where a group of meteors are observed to radiate from one point 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. A Lunar meteorite is a Meteorite that is known to have originated on the Moon. A Mars meteorite is a Meteorite that has landed on Earth and originated from Mars.

Orbit

Meteoroids and asteroids orbit around the Sun, in greatly differing orbits. Some of these objects orbit together in streams; these are probably comet remnants that would form a meteor shower. A meteor shower, some of which are known as a "meteor storm" or "meteor outburst" is a celestial event where a group of meteors are observed to radiate from one point Other meteoroids are not associated with any stream clustering (although there must also be meteoroids clustered in orbits which do not intercept Earth's or any other planet). The fastest objects travel at roughly 42 kilometers per second (26 miles per second) through space in the vicinity of Earth's orbit. Together with the Earth's orbital motion of 29 km/s (18 miles per second), collision speeds can reach 71 km/s (44 miles per second) during head-on collisions. This would only occur if the meteor were in a retrograde orbit. Direct motion is the motion of a Planetary body in a direction similar to that of other bodies within its system and is sometimes called prograde motion. Meteors have roughly a fifty percent chance of a daylight (or near daylight) collision with the Earth as the Earth orbits in the direction of roughly west at noon. Most meteors are however, observed at night as low light conditions allow fainter meteors to be observed. Meteors are usually seen when they are 60 to 120 km (40 to 75 miles) above the ground. ^[11]

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. The asteroid belt is the region of the Solar System located roughly between the orbits of the Planets Mars and Jupiter. ^[12]

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 broke up over the United States on October 9, 1992, an event witnessed by thousands across the Events 768 - Carloman I and Charlemagne are crowned Kings of The Franks. Year 1992 ( MCMXCII) was a Leap year starting on Wednesday (link will display full 1992 Gregorian calendar) ^[13]

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 (27 lb) and was subsequently identified as an H6 monomict breccia meteorite. ^[14] 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. The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into ^[15]

Gallery

A green and red Orionid meteor striking the sky below Milky Way and to the right of Venus. The Orionids are an annual meteor shower, named after their radiant which occurs in the Constellation Orion. The VENUS ( V ictoria E xperimental N etwork U nder the S ea project is a cabled sea floor observatory operated by the University Zodiacal light is also seen at the image. The zodiacal light is a faint roughly triangular whitish glow seen in the night sky which appears to extend up from the vicinity of the Sun along the Ecliptic	Orionid	Orionid	Two Orionids and Milky Way
Multi-colored Orionid	Orionid	The brightest meteor, a fireball, leaves a smokey persistent trail drifting in high-altitude winds, which is seen at the right-hand side of the image left by Orionid. The Orionids are an annual meteor shower, named after their radiant which occurs in the Constellation Orion. The Orionids are an annual meteor shower, named after their radiant which occurs in the Constellation Orion. The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Γαλαξίας (Galaxias sometimes referred to simply The Orionids are an annual meteor shower, named after their radiant which occurs in the Constellation Orion.

See also

• North American Meteor Network
• International Meteor Organization
• American Meteor Society (AMS)
• Baetylus
• Impact crater
• Meteor shower
• Meteorite
• Tektite
• Tollmann's hypothetical bolide
• Green fireballs
• Impact event

References

External links

• Astronomers spot meteor streaking across central Ontario sky - CBC News March 7, 2008
• 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