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10月22日 獵戶座流星雨極大預報
（2007年09月15日 14:09）
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□作者:
[1]
Orionids (ORI)
Active: October 2 —November 7
Maximum: October 21 (λ = 208°)
ZHR = 25
Radiant: α = 95°; δ = +16°
Radiant drift: see Table 6
v∞ = 66 km/s
r = 2.5
TFC: α = 100°; δ =+39° and
α = 75°; δ = +24° (β > 40° N) or
α = 80°; δ = +01° and
α = 117°; δ = +01° (β < 40° N)
The Orionid radiant, a little north of the celestial equator, is at a useful elevation by around local midnight in either hemisphere, somewhat before in the north, so most of the world can enjoy the shower. The waxing gibbous Moon will set by around 0h30m —2h30m for all observers this year, so leaving darker skies for much of the radiant's best-visible time. Audrius Dubietis' recent analysis of IMO data from 1984 —2001 showed some minor changes to past expectations, with the peak ZHR and r values varying somewhat from year to year. Maximum mean ZHRs ranged from ~ 14 —31 during the examined interval, with partial confirmation of a suspected 12-year periodicity in higher returns found earlier in the 20th century. This may mean stronger returns in 2008 —10, and perhaps best ZHRs of around 25 this year. The Orionids were always noted for having several lesser maxima other than the main one above, helping activity sometimes to remain roughly constant for several consecutive nights centred on this peak. In 1993 and 1998, a submaximum about as strong as the normal peak was detected on October 17 —18 from Europe, for instance. All observers should be aware of these possibilities, as observing circumstances are particularly favourable for covering the Orionids on both October 17 and 18 under dark skies in 2007. Several visual subradiants were reported in the past, but recent video work suggests the radiant is far less complex; more imaging and telescopic work to confirm this would be useful, as visual observers have clearly had problems with the shower's radiant determination before.
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責任編輯:skylook
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上一篇︰10月19日 雙子座ε流星雨極大預報
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