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An Earth-grazing fireball (or Earth-grazer)〔(【引用サイトリンク】title=APOD: 2009 March 2 - Earthgrazer: The Great Daylight Fireball of 1972 ). Antwrp.gsfc.nasa.gov. Retrieved on 2013-10-19.〕 is a fireball, a very bright meteor that enters Earth’s atmosphere and leaves again. Some fragments may impact Earth as meteorites, if the meteor starts to break up or explodes in mid-air. These phenomena are then called Earth-grazing meteor processions and bolides.〔 Famous examples of Earth-grazers are the 1972 Great Daylight Fireball and the Meteor Procession of July 20, 1860.〔(【引用サイトリンク】title=Texas State astronomers solve Walt Whitman meteor mystery : University News Service : Texas State University ). Txstate.edu (2010-05-28). Retrieved on 2013-10-19.〕〔(Images of Harper's Weekly front page story )〕〔(150-year-old meteor mystery solved )〕 == Overview == As an Earth-grazer passes through the atmosphere its mass and velocity are changed, so that its orbit, as it re-enters space, will be different from its orbit as it encountered Earth's atmosphere.〔(US19720810 (Daylight Earth grazer) ) Global Superbolic Network Archive, 2000, 'Size: 5 to 10 m'〕〔(Daylight Fireball of August 10, 1972 ) C. Kronberg, Munich Astro Archive, archived summary by Gary W. Kronk of early analysis and of Zdeněk Ceplecha's paper for Astronomy and Astrophysics in 1994, '3 meters, if a carbonaceous chondrite, or as large as 14 meters, if composed of cometary materials', 'post-encounter ... 2 or 10 meters'〕〔 There is no exact criterion for passing by outside of the atmosphere, except perhaps roughly up, or the Kármán line at . There is no agreed-upon end to the upper atmosphere, but rather incrementally thinner air from the stratosphere (~50 km), mesosphere (~85 km), and thermosphere (~690 km) up to the exosphere (~10,000) (see also thermopause). For example, a meteoroid can become a meteor at an altitude of 85–120 km above the Earth. The term Earth-grazer or inner-grazer is also sometimes used for an asteroid or meteoroid whose orbit brings it close to Earth (such as within a Lunar distance). A small Solar System body with a grazing orbit does not necessarily make contact with the Earth's atmosphere, although it may be more likely to collide with it (see List of Earth-crossing minor planets and Outer-grazer). 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「Earth-grazing fireball」の詳細全文を読む スポンサード リンク
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