1972年白日大火球
1972年白日大火球（或編號 US19720810）是一個於UTC 1972年8月10日20:29 掠過地球57公里高空的掠地流星體。該天體在當時是白晝的美國猶他州（當地時間 14:30）直到北方的加拿大亞伯達省都有人目擊。該火球被許多人錄下影像[2]。
描述
當時分析該火球的影像和路徑後認為該流星體的大小是在3公尺（如果是碳質球粒隕石）到14公尺（如果是從彗星剝落的含冰物質）[3][4]的地球軌道穿越小行星中的阿波羅型小行星，並認為下次接近地球時間是1997年8月[2]。1994年捷克天文學家茲德內克·賽普爾查（Zdeněk Ceplecha）重新分析相關資料，該物體質量估計降為先前的二分之一到三分之一，其體積估計則為 2 至 10 公尺[3]。
該流星體掠過地球大氣層 100 秒之中的速度則降為 800 m/s，因此其軌道傾角也自角度 15 度改為 8 度[4]。
US19720810 流星體在亞瑟·查理斯·克拉克的小說《上帝之鎚》第一章前言中被提及。
如果該天體撞擊地球？
如果該天體的擦地角有所改變，該天體可能在高空失速，可能結果就是在空中爆炸，並有部分碎片以終端速度掉落。流星體進入大氣層後的運動相當複雜，並且需要完整的模擬才能計算；但在網路上也有加雷思·柯林斯（Gareth Collins）等人[5]開發的大幅簡化的計算模式可供估計撞擊能量[6]。下表顯示在不同進入大氣層角度和成份下的不同結果：
| 直徑（m） | 密度（cm3） | 進入大氣層角度（°） | 喪失能量（kt） | 爆炸高度（km） | 爆炸能量（kt） |
|---|---|---|---|---|---|
| 3 | 3.4 | 1 degree | 1.3 kiloton | 43 km | 0.7 kiloton |
| 3 | 3.4 | 45 degrees | 1.3 kiloton | 39 km | 0.4 kiloton |
| 8 | 0.9 | 1 degree | 6 kiloton | 80 km | 0.4 kiloton |
| 8 | 0.9 | 45 degrees | 6 kiloton | 45 km | 2 kiloton |
參考資料
- Astronomy Picture of the Day. 2009 March 2.
- Observation of Meteoroid Impacts by Space-Based Sensors 页面存档备份，存于 Astronomical Society of the Pacific, Edward Tagliaferri, 2003, 'It was first detected by satellite at an altitude of about 73 km, tracked as it descended to about 53 km, and then tracked as it climbed back out of the atmosphere', 'object is still in an Earth-crossing orbit around the Sun and passed close to the Earth again in August 1997'
- Daylight Fireball of August 10, 1972 C. Kronberg, Munich Astro Archive, archived summary by Gary W. Kronk of early analysis and of Zdenek 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'
- US19720810 (Daylight Earth grazer) 页面存档备份，存于 Global Superbolic Network Archive, 2000, 'Size: 5 to 10 m'
- Collins, Gareth S. et al. Earth Impact Effects Program: A Web-based computer program for calculating the regional environmental consequences of a meteoroid impact on Earth 页面存档备份，存于 Meteoritics & Planetary Science 40, Nr 6, 817–840 (2005) "The curvature of the Earth is also ignored."
- Robert Marcus, H. Jay Melosh, and Gareth Collins. Computing Effects of an Impact on Earth 页面存档备份，存于
- Abe, S. et al. (abstract) Earth-grazing fireball on March 29, 2006页面存档备份，存于 European Planetary Science Congress 2006. Berlin, Germany, 18 - 22 September 2006., p.486. code:2006epsc.conf..486A, 'the first and second Earth-grazing fireballs observed on August 10, 1972(Jacchia, 1974; Ceplecha, 1979) and on October 13, 1990(Borovicka and Ceplecha, 1992)'
- Abe, Shinsuke; et al. 2006. (PDF). Earth-grazing fireball on March 29, 2006页面存档备份，存于 (full details: orbit, charts, spectra, composition) Retrieved 2008-07-07
外部連結
- Youtube上懷俄明州目擊者錄影页面存档备份，存于
- Youtube上亞伯達省目擊者錄影页面存档备份，存于
- US19720810 (Daylight Earth grazer) orbital characteristics from Global Superbolide Network Archive, 2000
- fireball, meteorite, bolide, meteor, video and photo页面存档备份，存于 link to photos and cine film by Linda Baker
- Earthgrazer: The Great Daylight Fireball of 1972页面存档备份，存于 overview of the event including photo by NASA's Astronomy Picture of the Day
- Astronomical Society of the Pacific: Observation of Meteoroid Impacts by Space-Based Sensors - one of several similar events; includes ground track
- 每日一天文圖 (成大物理分站) 2009年3月2日
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