Editing Impact event (section)

====20th-century impacts====
[[File:Tunguska Ereignis-1.jpg|thumb|Trees knocked over by the [[Tunguska event|Tunguska blast]]]]

One of the best-known recorded impacts in modern times was the Tunguska event, which occurred in [[Siberia]], Russia, in 1908.<ref>{{cite web|title=Tunguska event {{!}} Summary, Cause, & Facts|url=https://www.britannica.com/event/Tunguska-event|access-date=2021-09-25|website=Encyclopedia Britannica|language=en}}</ref> This incident involved an explosion that was probably caused by the airburst of an asteroid or comet {{convert|5|to|10|km|mi|abbr=on}} above the Earth's surface, [[felling]] an estimated 80 million trees over {{convert|2150|km2|mi2|0|abbr=on}}.<ref>{{cite web|url=http://www.bbc.com/earth/story/20160706-in-siberia-in-1908-a-huge-explosion-came-out-of-nowhere|title=In Siberia in 1908, a huge explosion came out of nowhere|last=Hogenboom|first=Melissa|access-date=2017-03-30}}</ref>

In February 1947, another large bolide impacted the Earth in the [[Sikhote-Alin Mountains]], [[Primorsky Krai|Primorye]], Soviet Union. It was during daytime hours and was witnessed by many people, which allowed [[V. G. Fesenkov]], then chairman of the meteorite committee of the USSR Academy of Science, to estimate the meteoroid's orbit before it encountered the Earth. [[Sikhote-Alin meteorite|Sikhote-Alin]] is a massive fall with the overall size of the [[meteoroid]] estimated at {{convert|90000|kg|lb|abbr=on}}. A more recent estimate by Tsvetkov (and others) puts the mass at around {{convert|100000|kg|lb|abbr=on}}.<ref name="metmag">{{cite journal |url=http://meteoritemag.uark.edu/604.htm |journal=Meteorite Magazine | date=February 1996 |title=Sikhote-Alin Revisited |first=Roy |last=Gallant |volume=2 |page=8 |bibcode=1996Met.....2....8G |archive-url=https://web.archive.org/web/20100612144717/http://meteoritemag.uark.edu/604.htm |archive-date=2010-06-12 |url-status=dead }}</ref> It was an iron meteorite belonging to the chemical group IIAB and with a coarse octahedrite structure. More than 70 [[tonne]]s ([[metric ton]]s) of material survived the collision.

A case of a human injured by a space rock occurred on November 30, 1954, in [[Sylacauga, Alabama]].<ref>[http://imca.repetti.net/metinfo/metstruck.html Meteorite Hits Page] {{webarchive |url=https://web.archive.org/web/20090831183851/http://imca.repetti.net/metinfo/metstruck.html |date=August 31, 2009 }}</ref> There a {{convert|4|kg|lb|abbr=on}} stone chondrite crashed through a roof and hit Ann Hodges in her living room after it bounced off her radio. She was badly bruised by the [[Hodges Meteorite#Fragments|fragments]]. Several persons have since claimed to have been struck by "meteorites" but no verifiable meteorites have resulted.

A small number of [[meteorite fall]]s have been observed with automated cameras and recovered following calculation of the impact point. The first was the [[Příbram meteorite]], which fell in Czechoslovakia (now the Czech Republic) in 1959.<ref>{{Citation |last=Ceplecha |first=Z. |date=1961 |title=Multiple fall of Příbram meteorites photographed |journal=Bull. Astron. Inst. Czechoslovakia |volume=12 |pages=21–46 |bibcode=1961BAICz..12...21C }}</ref> In this case, two cameras used to photograph meteors captured images of the fireball. The images were used both to determine the location of the stones on the ground and, more significantly, to calculate for the first time an accurate orbit for a recovered meteorite.

Following the Příbram fall, other nations established automated observing programs aimed at studying infalling meteorites.<ref>Gritsevich, M.I. The Pribram, Lost City, Innisfree, and Neuschwanstein falls: An analysis of the atmospheric trajectories. Sol Syst Res 42, 372–390 (2008). https://doi.org/10.1134/S003809460805002X</ref> One of these was the [[Prairie Meteorite Network]], operated by the [[Smithsonian Astrophysical Observatory]] from 1963 to 1975 in the midwestern U.S. This program also observed a meteorite fall, the "Lost City" chondrite, allowing its recovery and a calculation of its orbit.<ref>{{Citation |last1=McCrosky |first1=R. E. |last2=Posen |first2=A. |last3=Schwartz |first3=G. |last4=Shao |first4=C. Y. |date=1971 |title=Lost City meteorite: Its recovery and a comparison with other fireballs |journal=J. Geophys. Res. |volume=76 |issue= 17|pages=4090–4108 |doi=10.1029/JB076i017p04090 |bibcode=1971JGR....76.4090M|hdl=2060/19710010847 |s2cid=140675097 |hdl-access=free }}</ref> Another program in Canada, the Meteorite Observation and Recovery Project, ran from 1971 to 1985. It too recovered a single meteorite, "Innisfree", in 1977.<ref>{{Citation |last1=Campbell-Brown |first1=M. D. |last2=Hildebrand |first2=A. |date=2005 |title=A new analysis of fireball data from the Meteorite Observation and Recovery Project (MORP) |journal=Earth, Moon, and Planets |volume=95 |issue=1–4 |pages=489–499 |doi=10.1007/s11038-005-0664-9 |bibcode = 2004EM&P...95..489C |s2cid=121255827 }}</ref> Finally, observations by the European Fireball Network, a descendant of the original Czech program that recovered Příbram, led to the discovery and orbit calculations for the [[Neuschwanstein]] meteorite in 2002.<ref>{{Citation |last1=Oberst |first1=J. |date=2004 |title=The multiple meteorite fall of Neuschwanstein: Circumstances of the event and meteorite search campaigns |journal=[[Meteoritics & Planetary Science]] |volume=39 |issue=10 |pages=1627–1641 |doi=10.1111/j.1945-5100.2004.tb00062.x |bibcode=2004M&PS...39.1627O |display-authors=2 |last2=Heinlein |first2=D. |last3=Spurný |first3=P.|doi-access=free }}</ref>

On August 10, 1972, a meteor which became known as the [[1972 Great Daylight Fireball]] was witnessed by many people as it moved north over the [[Rocky Mountains]] from the U.S. Southwest to Canada. It was filmed by a tourist at the [[Grand Teton National Park]] in [[Wyoming]] with an 8-millimeter color movie camera.<ref>{{YouTube|7M8LQ7_hWtE|Grand Teton Meteor Video}}</ref> In size range the object was roughly between a car and a house, and while it could have ended its life in a Hiroshima-sized blast, there was never any explosion. Analysis of the trajectory indicated that it never came much lower than {{convert|58|km|mi|0|abbr=on}} off the ground, and the conclusion was that it had grazed Earth's atmosphere for about 100 seconds, then skipped back out of the atmosphere and returned to its orbit around the Sun.

Many impact events occur without being observed by anyone on the ground. Between 1975 and 1992, American missile [[early warning satellite]]s picked up 136 major explosions in the upper atmosphere.<ref>{{Cite web|url=http://www.aerospaceweb.org/question/astronomy/q0296.shtml|title= Collisions with Near Earth Objects|website=www.aerospaceweb.org}}</ref> In the November 21, 2002, edition of the journal ''Nature'', Peter Brown of the University of Western Ontario reported on his study of U.S. early warning satellite records for the preceding eight years. He identified 300 flashes caused by {{convert|1|to|10|m|ft|0|abbr=on}} meteors in that time period and estimated the rate of Tunguska-sized events as once in 400 years.<ref>[https://archive.today/20120910052024/http://www.spaceref.com/news/viewpr.html?pid=9865 Satellite Study Establishes Frequency of Megaton-sized Asteroid Impacts] (SpaceRef November 20, 2002)</ref> [[Eugene Shoemaker]] estimated that an event of such magnitude occurs about once every 300 years, though more recent analyses have suggested he may have overestimated by an order of magnitude.

In the dark morning hours of January 18, 2000, a [[Tagish Lake (meteorite)|fireball]] exploded over the city of [[Whitehorse, Yukon Territory]] at an altitude of about {{convert|26|km|mi|0|abbr=on}}, lighting up the night like day. The meteor that produced the fireball was estimated to be about {{convert|4.6|m|ft|abbr=on}} in diameter, with a weight of 180 tonnes. This blast was also featured on the Science Channel series ''Killer Asteroids'', with several witness reports from residents in [[Atlin, British Columbia]].