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A meteor shower is a celestial event in which a number of meteors are observed to radiate, or originate, from one point in the night sky. These meteors are caused by streams of cosmic debris called meteoroids entering Earth's atmosphere at extremely high speeds on parallel trajectories. Most meteors are smaller than a grain of sand, so almost all of them disintegrate and never hit the Earth's surface. Intense or unusual meteor showers are known as meteor outbursts and meteor storms, which may produce greater than 1,000 meteors an hour. The Meteor Data Center lists about 600 suspected meteor showers of which about 100 are well established.〔(Meteor Data Center list of Meteor Showers )〕 ==Historical developments== The first great storm in modern times was the Leonids of November 1833. One estimate is over one hundred thousand meteors an hour,〔(Space.com ) The 1833 Leonid Meteor Shower: A Frightening Flurry〕 but another, done as the storm abated, estimated in excess of two hundred thousand meteors an hour〔(Leonid MAC ) Brief history of the Leonid shower〕 over the entire region of North America east of the Rocky Mountains. American Denison Olmsted (1791−1859) explained the event most accurately. After spending the last weeks of 1833 collecting information he presented his findings in January 1834 to the American Journal of Science and Arts, published in January–April 1834, and January 1836. He noted the shower was of short duration and was not seen in Europe, and that the meteors radiated from a point in the constellation of Leo and he speculated the meteors had originated from a cloud of particles in space.〔(Observing the Leonids ) Gary W. Kronk〕 Work continued, however, coming to understand the annual nature of showers though the occurrences of storms perplexed researchers.〔(F.W. Russell, Meteor Watch Organizer ), by Richard Taibi , May 19, 2013, accessed 21 May 2013〕 In the 1890s, Irish astronomer George Johnstone Stoney (1826–1911) and British astronomer Arthur Matthew Weld Downing (1850–1917), were the first to attempt to calculate the position of the dust at Earth's orbit. They studied the dust ejected in 1866 by comet 55P/Tempel-Tuttle in advance of the anticipated Leonid shower return of 1898 and 1899. Meteor storms were anticipated, but the final calculations showed that most of the dust would be far inside of Earth's orbit. The same results were independently arrived at by Adolf Berberich of the Königliches Astronomisches Rechen Institut (Royal Astronomical Computation Institute) in Berlin, Germany. Although the absence of meteor storms that season confirmed the calculations, the advance of much better computing tools was needed to arrive at reliable predictions. In 1981 Donald K. Yeomans of the Jet Propulsion Laboratory reviewed the history of meteor showers for the Leonids and the history of the dynamic orbit of Comet Tempel-Tuttle. A graph 〔(http://web.archive.org )〕 from it was adapted and re-published in Sky and Telescope.〔(Comet 55P/Tempel-Tuttle and the Leonid Meteors )(1996, see p. 6)〕 It showed relative positions of the Earth and Tempel-Tuttle and marks where Earth encountered dense dust. This showed that the meteoroids are mostly behind and outside the path of the comet, but paths of the Earth through the cloud of particles resulting in powerful storms were very near paths of nearly no activity. In 1985, E. D. Kondrat'eva and E. A. Reznikov of Kazan State University first correctly identified the years when dust was released which was responsible for several past Leonid meteor storms. In 1995, Peter Jenniskens predicted the 1995 Alpha Monocerotids outburst from dust trails.〔Article published in 1997, notes prediction in 1995 - 〕 In anticipation of the 1999 Leonid storm, Robert H. McNaught,〔(Re: (meteorobs) Leonid Storm? ) By Rob McNaught,〕 David Asher,〔(Blast from the Past Armagh Observatory press release ) 1999 April 21st.〕 and Finland's Esko Lyytinen were the first to apply this method in the West.〔(Royal Astronomical Society Press Notice ) Ref. PN 99/27, Issued by: Dr Jacqueline Mitton RAS Press Officer〕〔(Voyage through a comet's trail, The 1998 Leonids sparkled over Canada ) By BBC Science's Dr Chris Riley on board NASA's Leonid mission〕 In 2006 Jenniskens has published predictions for future dust trail encounters covering the next 50 years.〔 Jérémie Vaubaillon continues to update predictions based on observartions each year for the Institut de Mécanique Céleste et de Calcul des Éphémérides (IMCCE).〔(IMCCE Prediction page )〕 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「Meteor shower」の詳細全文を読む スポンサード リンク
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