The Great Daylight 1972 Fireball (or US19720810) is an Earth grazer meteoroid which passed within 57 kilometres of the surface of the Earth at 20:29 UTC on August 10, 1972. 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 and recorded on film and by space borne sensors.
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 3 (if a carbonaceous chondrite) to 14 metres (if made of cometary ices) in diameter in the Apollo asteroid class in an Earth-crossing orbit that would make a subsequent close approach to Earth in August 1997. 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 (reducing its diameter to 2 to 10 metres).
The meteoroid's 100 second passage through the atmosphere reduced its velocity by about 800 metre per second and the whole encounter significantly changed its orbital inclination from 15 degrees to 8 degrees.
This was the first Earth grazing fireball observed. As of 2008 only three subsequent Earth grazers have been seen: the Earth-grazing fireball of October 13, 1990 passing at around 100 kilometres altitude over Czechoslovakia; the possible Earth-grazing fireball on March 29, 2006 over Japan, and EN070807 (see All known Earth-grazing fireballs).
 What if it had impacted?
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. 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.
Note: this took place in Grand Teton National Park, I couldn't find an exact city so I just stuck Salt Lake City in, based on the path of the meteor. Meteor Path
Source: [ur="http://en.wikipedia.org/wiki/The_Great_Daylight_1972_Fireball"]Wikipedia Article[/url]
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