Radiation astronomy/Fieries

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This is a fireball meteor trail with some burning still visible above the Urals city of Chelyabinsk, Russia, on February 15, 2013. Credit: Reuters/www.chelyabinsk.ru.

Above is a visual astronomy image of a fireball trail with some burning still visible from a meteor as it passed overhead in Chelyabinsk, Russia, on February 15, 2013.

This image shows "[t]he trail of a falling object ... seen above the Urals city of Chelyabinsk [on] February 15, 2013".[1]

Fireballs[edit]

This meteor image of October 17, 2012, is prior to the meteorite fall on the same day. Credit: Paola-Castillo; and Petrus M. Jenniskens, SETI Institute/NASA ARC.

A fireball is a brighter-than-usual meteor. The International Astronomical Union defines a fireball as "a meteor brighter than any of the planets" (magnitude −4 or greater).[2] 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.[3]

For 2011 there are 4589 fireballs records at the American Meteor Society.[4]

At right is a cell phone camera image of the green fireball over San Mateo, California, that left meteorite fragments. "The asteroid entered at a speed of 14 km/s, typical but on the slow side of other meteorite falls for which orbits were determined. ... The orbit in space is also rather typical: perihelion distance close to Earth's orbit (q = 0.987 AU) and a low-inclination orbit (about 5 degrees). ... 2012, October 17 - At 7:44:29 pm PDT this evening, a bright fireball was seen in the San Francisco Bay Area."[5]

"At 66 kilometers (41 miles) per second, they appear as fast streaks, faster by a hair than their sisters, the Eta Aquarids of May. And like the Eta Aquarids, the brightest of family tend to leave long-lasting trains. Fireballs are possible three days after maximum."[6]

Bolides[edit]

This diagram maps the data gathered from 1994-2013 on small asteroids impacting Earth's atmosphere. Credit: NASA/Planetary Science.

Def. a fireball reaching magnitude −14 or brighter.[7] is called a bolide.

"This diagram [center] maps the data gathered from 1994-2013 on small asteroids impacting Earth's atmosphere to create very bright meteors, technically called "bolides" and commonly referred to as "fireballs". Sizes of red dots (daytime impacts) and blue dots (nighttime impacts) are proportional to the optical radiated energy of impacts measured in billions of Joules (GJ) of energy, and show the location of impacts from objects about 1 meter (3 feet) to almost 20 meters (60 feet) in size."[8]

"A map released [...] by NASA's Near Earth Object (NEO) Program reveals that small asteroids frequently enter and disintegrate in the Earth's atmosphere with random distribution around the globe. Released to the scientific community, the map visualizes data gathered by U.S. government sensors from 1994 to 2013. The data indicate that Earth's atmosphere was impacted by small asteroids, resulting in a bolide (or fireball), on 556 separate occasions in a 20-year period. Almost all asteroids of this size disintegrate in the atmosphere and are usually harmless. The notable exception was the Chelyabinsk event which was the largest asteroid to hit Earth in this period."[8]

Superbolides[edit]

Def. a fireball reaching an magnitude −17 or brighter is called a superbolide.

Earth-grazing fireballs[edit]

A relatively small percentage of meteoroids hit the Earth's atmosphere and then pass out again: these are termed Earth-grazing fireballs (for example The Great Daylight 1972 Fireball).

Visuals[edit]

A meteor is the visible path of a meteoroid that has entered the Earth's atmosphere.

There are many definitions of a meteor ranging from any atmospheric phenomenon to a fast-moving streak of light in the night sky caused by the entry of extraterrestrial matter into the earth's atmosphere: A shooting star or falling star.

Meteors become visible between about 75 to 120 kilometers (34 - 70 miles) above the Earth. They disintegrate at altitudes of 50 to 95 kilometers (31-51 miles). Most meteors are observed at night, when darkness allows fainter objects to be recognized. Most meteors glow for about a second.

References[edit]

  1. Lua error in Module:Citation/CS1 at line 3723: bad argument #1 to 'pairs' (table expected, got nil).
  2. MeteorObs Explanations and Definitions (states IAU definition of a fireball). Meteorobs.org. 1999-07-09. Retrieved 2011-09-16.
  3. International Meteor Organization - Fireball Observations. Imo.net. 2004-10-12. Retrieved 2011-09-16.
  4. Fireball Report: 4589 records found between 2011-01-01 and 2011-12-31. American Meteor Society. Retrieved 2012-04-24.
  5. Lua error in Module:Citation/CS1 at line 3723: bad argument #1 to 'pairs' (table expected, got nil).
  6. David Levy and Stephen Edberg. Observe: Meteors. Astronomical League. |access-date= requires |url= (help)
  7. MJS Belton (2004). Mitigation of hazardous comets and asteroids. Cambridge University Press. ISBN 0-521-82764-7.:156
  8. 8.0 8.1 Lua error in Module:Citation/CS1 at line 3723: bad argument #1 to 'pairs' (table expected, got nil).