The Great Daylight 1972 Fireball

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The Great Daylight 1972 Fireball (or US19720810) is an Earth grazer meteoroid which passed within 57 km of the surface of the Earth at 20:29 UTC on August 10, 1972, or 1.01 Earth radii from the centre of the Earth. It entered the Earth's atmosphere in daylight over Utah, United States (1430 local time) and passed northwards leaving the atmosphere over Alberta, Canada. It was seen by many people, recorded on film and by space borne sensors.^[1]

By comparison, the Otto C. Winzen developed balloon reached 51.8 kilometres in 1972 and Low Earth Orbit satellites orbit from about 200 kilometres from the surface of the Earth.

Analysis of its appearance and trajectory showed it was a meteoroid about 2 to 10 metres^[2]^[3] in diameter in the Apollo asteroid class in an orbit that would make a subsequent close approach to Earth in August 1997.^[1] In 1994 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.^[2]

The meteoroid's 100 second passage through the atmosphere reduced its velocity by about 800 metres per second and the whole encounter significantly changed its orbital inclination from 15 degrees to 8 degrees.^[3]

This was the first Earth grazing fireball observed. As of 2006 only two subsequent Earth grazers have been seen: the Earth-grazing fireball of October 13, 1990 passing at around 100 kilometres altitude over Czechoslovakia; and the possible Earth-grazing fireball on March 29, 2006 over Japan.^[4]

[edit] See also

Record-setting close approaches by asteroids to Earth

[edit] Notes

^ ^a ^b Observation of Meteoroid Impacts by Space-Based Sensors Astronomical Society of the Pacific, Edward Tagliaferri, 2003, 'It was first detected by satellite at an altitude of about 73 km, tracked as it descended to about 53 km, and then tracked as it climbed back out of the atmosphere', 'object is still in an Earth-crossing orbit around the Sun and passed close to the Earth again in August 1997'
^ ^a ^b Daylight Fireball of August 10, 1972 C. Kronberg, Munich Astro Archive, archived summary by Gary W. Kronk of early analysis and of Zdenek Ceplecha's paper for Astronomy and Astrophysics in 1994, '3 meters, if a carbonaceous chondrite, or as large as 14 meters, if composed of cometary materials', 'post-encounter ... 2 or 10 meters'
^ ^a ^b US19720810 (Daylight Earth grazer) Global Superbolic Network Archive, 2000, 'Size: 5 to 10 m'
^ Earth-grazing fireball on March 29, 2006 Abe, S. et al, code:2006epsc.conf..486A, 'the first and second Earth-grazing fireballs observed on August 10 1972(Jacchia, 1974; Ceplecha, 1979) and on October 13 1990(Borovicka and Ceplecha, 1992)'

[edit] References

US19720810 (Daylight Earth grazer) orbital characteristics from Global Superbolide Network Archive, 2000
fireball, meteorite, bolide, meteor, video and photo link to photos and cine film by Linda Baker
The Great Daylight 1972 Fireball youtube link to Linda Baker's film

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