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The Tunguska event was a large explosion that occurred near the Stony Tunguska River, in what is now Krasnoyarsk Krai, Russia, on the morning of 30 June 1908 (N.S.).〔 The explosion over the sparsely populated Eastern Siberian Taiga flattened of forest and caused no known casualties. The cause of the explosion is generally thought to have been a meteor. It is classified as an impact event, even though no impact crater has been found; the meteor is thought to have burst in mid-air at an altitude of rather than hit the surface of the Earth.〔(【引用サイトリンク】title=APOD: 2007 November 14 – Tunguska: The Largest Recent Impact Event )〕 Different studies have yielded varying estimates of the superbolide's size, on the order of , depending on whether the meteor was a comet or a denser asteroid. It is considered the largest impact event on Earth in recorded history. Since the 1908 event, there have been an estimated 1,000 scholarly papers (mainly in Russian) published on the Tunguska explosion. Many scientists have participated in Tunguska studies: the best known are Leonid Kulik, Yevgeny Krinov, Kirill Florensky, Nikolai Vladimirovich Vasiliev, and Wilhelm Fast. In 2013, a team of researchers led by Victor Kvasnytsya of the National Academy of Sciences of Ukraine published analysis results of micro-samples from a peat bog near the center of the affected area showing fragments that may be of meteoritic origin. Estimates of the energy of the air burst range from 30 megatons of TNT (130 PJ) to ,〔 depending on the exact height of burst estimated when the scaling-laws from the effects of nuclear weapons are employed. More modern supercomputer calculations that include the effect of the object's momentum estimate that the airburst had an energy range from 3 to 5 megatons of TNT (13 to 21 PJ), and that simply more of this energy was focused downward than would be the case from a nuclear explosion.〔 Using the 15 megaton nuclear explosion derived estimate is an energy about 1,000 times greater than that of the atomic bomb dropped on Hiroshima, Japan; roughly equal to that of the United States' Castle Bravo ground-based thermonuclear test detonation on 1 March 1954; and about two-fifths that of the Soviet Union's later Tsar Bomba (the largest nuclear weapon ever detonated).〔Verma (2005), p 1.〕 It is estimated that the Tunguska explosion knocked down some 80 million trees over an area of , and that the shock wave from the blast would have measured 5.0 on the Richter scale. An explosion of this magnitude would be capable of destroying a large metropolitan area, but due to the remoteness of the location, no fatalities were documented. This event has helped to spark discussion of asteroid impact avoidance. ==Description== At around 7:17 a.m. local time, Evenki 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 ten minutes later, there was a flash and a sound similar to artillery fire. Eyewitnesses closer to the explosion reported that the source of the sound moved from the east to the north of them. 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 did not report seeing the explosion. Eyewitness accounts vary regarding the sequence and duration of the events. The explosion registered at seismic stations across Eurasia. It is estimated that, in some places, the resulting shock wave was equivalent to an earthquake measuring 5.0 on the Richter scale.〔Traynor, Chris, "The Tunguska Event", ''Journal of the British Astronomical Association'', 107, 3, 1997〕 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;〔Watson, Nigel. "The Tunguska Event". ''History Today'' 58.1 (July 2008): 7. MAS Ultra-School Edition. EBSCO. 10 February 2009 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tunguska event」の詳細全文を読む スポンサード リンク
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