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The Great Daylight 1972 Fireball (or US19720810) is an Earth-grazing meteoroid
Meteoroid

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 Earth's atmosphere is called a meteor, or commonly a "shooting star" or "falling star"....
 which passed within 57 kilometres (35.4 miles) of the surface of the Earth at 20:29 UTC on August 10 1972. It entered the Earth's atmosphere in daylight over Utah
Utah

The State of Utah is a western United States U.S. state of the United States. It was the List of U.S. states by date of statehood admitted to the United States on January 4, 1896....
, United States (14:30 local time) and passed northwards leaving the atmosphere over Alberta
Alberta

Alberta is one of Canada Canadian Prairies Provinces and territories of Canada. It became a province on September 1, 1905.Alberta is located in western Canada, bounded by the provinces of British Columbia to the west and Saskatchewan to the east, the Northwest Territories to the north, and the U.S....
, Canada. It was seen by many people and recorded on film and by space borne sensors.

ysis of its appearance and trajectory showed it was a meteoroid
Meteoroid

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 Earth's atmosphere is called a meteor, or commonly a "shooting star" or "falling star"....
 about (if a carbonaceous chondrite
Carbonaceous chondrite

Carbonaceous chondrites or C chondrites are a class of chondrite meteorites comprising at least 8 known groups and many ungrouped meteorites....
) to (if made of comet
Comet

A comet is a Small Solar System body that orbits the Sun and, when close enough to the Sun, exhibits a visible coma or a tail?both primarily from the effects of solar radiation upon the Comet nucleus....
ary ices) in diameter in the Apollo asteroid
Apollo asteroid

The Apollo asteroids are a group of near-Earth asteroids named after 1862 Apollo, the first asteroid of this group to be discovered by Karl Wilhelm Reinmuth....
 class in an Earth-crossing orbit
Earth-crosser asteroid

An Earth-crosser asteroid is a Near-Earth asteroid whose orbit crosses that of Earth. The known numbered Earth-crossers are listed here. Those Earth-crossers whose semimajor axis are smaller than Earth's are Aten asteroids; the remaining ones are Apollo asteroids....
 that would make a subsequent close approach to Earth in August 1997.






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The Great Daylight 1972 Fireball (or US19720810) is an Earth-grazing meteoroid
Meteoroid

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 Earth's atmosphere is called a meteor, or commonly a "shooting star" or "falling star"....
 which passed within 57 kilometres (35.4 miles) of the surface of the Earth at 20:29 UTC on August 10 1972. It entered the Earth's atmosphere in daylight over Utah
Utah

The State of Utah is a western United States U.S. state of the United States. It was the List of U.S. states by date of statehood admitted to the United States on January 4, 1896....
, United States (14:30 local time) and passed northwards leaving the atmosphere over Alberta
Alberta

Alberta is one of Canada Canadian Prairies Provinces and territories of Canada. It became a province on September 1, 1905.Alberta is located in western Canada, bounded by the provinces of British Columbia to the west and Saskatchewan to the east, the Northwest Territories to the north, and the U.S....
, Canada. It was seen by many people and recorded on film and by space borne sensors.

Description

Analysis of its appearance and trajectory showed it was a meteoroid
Meteoroid

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 Earth's atmosphere is called a meteor, or commonly a "shooting star" or "falling star"....
 about (if a carbonaceous chondrite
Carbonaceous chondrite

Carbonaceous chondrites or C chondrites are a class of chondrite meteorites comprising at least 8 known groups and many ungrouped meteorites....
) to (if made of comet
Comet

A comet is a Small Solar System body that orbits the Sun and, when close enough to the Sun, exhibits a visible coma or a tail?both primarily from the effects of solar radiation upon the Comet nucleus....
ary ices) in diameter in the Apollo asteroid
Apollo asteroid

The Apollo asteroids are a group of near-Earth asteroids named after 1862 Apollo, the first asteroid of this group to be discovered by Karl Wilhelm Reinmuth....
 class in an Earth-crossing orbit
Earth-crosser asteroid

An Earth-crosser asteroid is a Near-Earth asteroid whose orbit crosses that of Earth. The known numbered Earth-crossers are listed here. Those Earth-crossers whose semimajor axis are smaller than Earth's are Aten asteroids; the remaining ones are Apollo asteroids....
 that would make a subsequent close approach to Earth in August 1997. In 1994, Czech astronomer Zdenek Ceplecha re-analysed the data and suggested the passage would have reduced the meteoroid's mass to about a third or half of its original mass (reducing its diameter to 2 to 10 metres).

The meteoroid's 100 second passage through the atmosphere reduced its velocity by about and the whole encounter significantly changed its orbital inclination
Inclination

Inclination in general is the angle between a reference plane and another plane or Axis_of_rotation of direction. The axial tilt is expressed as the angle made by the planet's axis and a line drawn through the planet's center perpendicular to the orbital plane....
 from 15 degrees to 8 degrees.

The fireball was filmed by a tourist at the Grand Teton National Park
Grand Teton National Park

Grand Teton National Park is a United States National Park located in northwestern Wyoming, south of Yellowstone National Park. The park is named after the Grand Teton, which, at , is the tallest mountain in the Teton Range....
 in Wyoming
Wyoming

The State of Wyoming is a sparsely populated U.S. state in the Northwestern United States of the United States. The majority of the state is dominated by the mountain ranges and rangelands of the Rocky Mountains, while the easternmost section of the state is a high altitude prairie region known as the High Plains ....
 using an 8-millimeter color movie camera.

What if it had collided?

If it had not entered at such a grazing angle, this meteoroid would have lost all its velocity in the upper atmosphere, possibly ending in an airburst, and any remnant would have fallen at terminal velocity
Terminal velocity

File:Terminal velocity.svgIn fluid dynamics an object is moving at its terminal velocity if its speed is constant due to the restraining force exerted by the air, water or other fluid in which it is moving....
. Atmospheric entry of meteoroids is complex and a full calculation requires a full simulation, but a highly simplified calculation can be made using the web-based program by Collins et al.. This table shows how sensitive the result is to the entry angle and composition:

DiameterDensityEntry angleEnergy lostAirburst altitudeAirburst energy
33.41 degree1.3 kiloton43 km0.7 kiloton
33.445 degrees1.3 kiloton39 km0.4 kiloton
80.91 degree6 kiloton80 km0.4 kiloton
80.945 degrees6 kiloton45 km2 kiloton


All known Earth-grazing fireballs

Earth-grazing fireballs are a very rare kind of fireball caused by a meteoroid that collides with the Earth but survives the collision by passing through, and exiting, the atmosphere. four grazers have been scientifically observed.

  • 1913-02-09, a narrow fireball stream led to conclusions a probable natural satellite
    Natural satellite

    A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called the primary. Technically, the term natural satellite could refer to a planet orbiting a star, or a dwarf galaxy orbiting a major galaxy, but it is normally synonymous with moon and used to identify non-artificial satellites...
     of Earth had broken up
  • 1972-08-10, US19720810
    The Great Daylight 1972 Fireball

    The Great Daylight 1972 Fireball is an Earth-grazing meteoroid which passed within 57 kilometres of the surface of the Earth at 20:29 UTC on August 10 1972....
     at 15 km/s above United States and Canada (first scientific observation)
  • 1990-10-13, a 40 kilogram, 41.5 km per sec meteoroid passed at 97.9 km above Czechoslovakia
  • 2006-03-29, fireball passed 18.8 km per sec through the atmosphere 71.4 km above Japan
  • 2007-08-07, EN070807 passed through with an orbit belonging to the rare Aten asteroid
    Aten asteroid

    The Aten asteroids are a group of near-Earth asteroids, named after the first of the group to be discovered . They are defined by having semi-major axis of less than one astronomical unit ....
     type


See also

  • Record-setting close approaches by asteroids to Earth
    List of noteworthy asteroids

    The following is a collection of lists of notable asteroids in the Solar System, including minor planets inside the orbit of Neptune. For a complete list of all minor planets in sequential numerical order, see List of minor planets....


External links

  • orbital characteristics from Global Superbolide Network Archive, 2000
  • link to photos and cine film by Linda Baker
  • youtube link to Linda Baker's film
  • An other film on youtube
  • overview of the event including photo by NASA's Astronomy Picture of the Day