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The October Draconids, in the past also unofficially known as the Giacobinids, are a meteor shower whose parent body is the periodic comet 21P/Giacobini-Zinner. They are named after the constellation Draco, where they seemingly come from. Almost all meteors which fall towards Earth ablate long before reaching its surface. The Draconids are best viewed after sunset in an area with a clear dark sky. The 1933 and 1946〔 Draconids had Zenithal Hourly Rates of thousands of meteors visible per hour, among the most impressive meteor storms of the 20th century. Rare outbursts in activity can occur when the Earth travels through a denser part of the cometary debris stream; for example, in 1998, rates suddenly spiked〔(【引用サイトリンク】url=http://science.nasa.gov/newhome/headlines/ast14oct98_2.htm )〕〔Arlt, R. ("Summary of 1998 Draconid Outburst Observations" ), ''WGN, Journal of the International Meteor Organization, Vol. 26, p. 256-259'', 1998.〕 and spiked again (less spectacularly) in 2005.〔Campbell-Brown, M.; Vaubaillon, J.; Brown, P.; Weryk, R. J.; Arlt, R. ("The 2005 Draconid outburst" ), ''Astronomy and Astrophysics, Volume 451, pp.339-344'', 2006.〕 A Draconid meteor outburst occurred〔(【引用サイトリンク】publisher=International Meteor Organization (IMO) )〕 as expected〔(【引用サイトリンク】url=http://www.imo.net/draconids2011 )〕 on 2011 October 8, though a waxing gibbous Moon reduced the number of meteors observed visually. During the 2012 shower radar observations detected up to 1000 meteors per hour. The 2012 outburst may have been caused by the narrow trail of dust and debris left behind by the parent comet in 1959. ==References== * Michael D. Reynolds. (''Falling Stars'' ). Stackpole Books, 2001. p.42. * Jun-Ichi Watanabe and Mikiya Sato. ("Activities of Parent Comets and Related Meteor Showers" ). Earth, Moon and Planets, Vol 102, No 1-4 (June 2008). p111-116. * (Draconids 2011 ephemerides ) 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「Draconids」の詳細全文を読む スポンサード リンク
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