通古斯大爆炸英文简介TungusExplosionPPT课件

2021/6/712021/6/72The Tunguska event,or Tunguska explosion,was an enormously powerful explosion that occurred near the Podkamennaya(Lower Stony)Tunguska River in what is now Krasnoyarsk Krai in Russia about 7:14 A.M.(0:14 Universal Time)on June 30,1908(June 17 in the Julian calendar,in use locally at the time).The explosion is believed to have been caused by the air burst of a large meteoroid or comet fragment at an altitude of 510 kilometres(3.16.2 mi)above the Earths surface.Different studies have yielded varying estimates of the objects size,with general agreement that it was a few tens of metres acrossThe number of scholarly publications on the problem of the Tunguska explosion since 1908 may be estimated at about 1,000(mainly in Russian).Many scientists have participated in Tunguska studies2021/6/73Although the meteoroid or comet burst in the air rather than hitting the surface,this event is still referred to as an impact.Estimates of the energy of the blast range from 5 to as high as 30 megatons of TNT(21130 PJ,with 1015 megatons of TNT(4263 PJ)the most likelyroughly equal to the United States Castle Bravo thermonuclear bomb tested on March 1,1954,about 1,000 times as powerful as the atomic bomb dropped on Hiroshima,Japan,and about one-third the power of the Tsar Bomba,the largest nuclear weapon ever detonated.The explosion knocked over an estimated 80 million trees covering 2,150 square kilometres(830 sq mi).It is estimated that the shock wave from the blast would have measured 5.0 on the Richter scale.An explosion of this magnitude is capable of destroying a large metropolitan area.This possibility has helped to spark discussion of asteroid deflection strategies.The Tunguska event is the largest impact event over land in Earths recent history.Impacts of similar size over remote ocean areas would have gone unnoticed before the advent of global satellite monitoring in the 1960s and 1970s.2021/6/74DescriptionApproximate location of the Tunguska event in SiberiaAt around 7:17 a.m.local time,Tungus natives and Russian settlers in the hills northwest of Lake Baikal observed a column of bluish light,nearly as bright as the Sun,moving across the sky.About 10 minutes later,there was a flash and a sound similar to artillery fire.Eyewitnesses closer to the explosion reported the sound source moving east to north.The sounds were accompanied by a shock wave that knocked people off their feet and broke windows hundreds of kilometres away.The majority of witnesses reported only the sounds and the tremors,and not the sighting of the explosion.Eyewitness accounts differ as to the sequence of events and their overall duration.The explosion registered on seismic stations across Eurasia.In some places the shock wave would have been equivalent to an earthquake of 5.0 on the Richter scale.12 It also produced fluctuations in atmospheric pressure strong enough to be detected in Great Britain.Over the next few days,night skies in Asia and Europe were aglow;13 it has been theorized that this was due to light passing through high-altitude ice particles formed at extremely cold temperatures,a phenomenon that occurs when the Space Shuttle re-enters the Earths atmosphere.1415 In the United States,the Smithsonian Astrophysical Observatory and the Mount Wilson Observatory observed a decrease in atmospheric transparency that lasted for several months,from suspended dust.2021/6/75Earth impactor modeledit Meteoroid airburstThe leading scientific explanation for the explosion is the airburst of a meteoroid 610 kilometres(46 miles)above Earths surface.citation neededMeteoroids enter Earths atmosphere from outer space every day,usually travelling at a speed of more than 10 kilometres per second(6 miles/sec or 21,600 mph).The heat generated by compression of air in front of the body(ram pressure)as it travels through the atmosphere is immense and most meteoroids burn up or explode before they reach the ground.Since the second half of the 20th century,close monitoring of Earths atmosphere has led to the discovery that such meteoroid airbursts occur rather frequently.A stony meteoroid of about 10 metres(30 ft)in diameter can produce an explosion of around 20 kilotons,similar to that of the Fat Man bomb dropped on Nagasaki,and data released by the U.S.Air Forces Defense Support Program indicate that such explosions occur high in the upper atmosphere more than once a year.Tunguska-like megaton-range events are much rarer.Eugene Shoemaker estimated that such events occur about once every 300 years.30312021/6/76Blast patternsThe explosions effect on the trees near ground zero was replicated during atmospheric nuclear tests in the 1950s and 1960s.These effects are caused by the shock wave produced by large explosions.The trees directly below the explosion are stripped as the blast wave moves vertically downward,while trees further away are knocked over because the blast wave is travelling closer to the horizontal when it reaches them.Soviet experiments performed in the mid-1960s,with model forests(made of matches on wire stakes)and small explosive charges slid downward on wires,produced butterfly-shaped blast patterns strikingly similar to the pattern found at the Tunguska site.The experiments suggested that the object had approached at an angle of roughly 30 degrees from the ground and 115 degrees from north and had exploded in mid-air.citation needed2021/6/77Speculative hypothesesThe behaviour of meteorites in the Earths atmosphere was less well understood during the early decades of the 20th century.Due to this,as well as the paucity of relevant data resulting from Soviet secrecy during the Cold War,a great many other hypotheses for the Tunguska event have sprung up,none of which are accepted by the scientific community.Comet 2005NB56 End of the world?Natural H-bomb Black hole Antimatter The Wardenclyffe Tower Alien spaceship crash Geophysical hypothesis 2021/6/78The endThe end部分资料从网络收集整理而来，供大家参考，感谢您的关注！