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英仙座流星雨IMO(国际流星组织)官方预测  

2007-07-27 17:45:29|  分类: 默认分类 |  标签: |举报 |字号 订阅

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Perseids (PER)

Active: July 17 —August 24
Maximum: August 13; 5h —7h30m UT (λ = 140°0 —140°1) - but see text
ZHR = 100
Radiant: α = 046°; δ = +58°
Radiant drift: see Table 6
v = 59 km/s; r = 2.6
TFC: α = 019°; δ = +38° and
α = 348°; δ = +74° before 2h local time
α = 043°; δ = +38° and
α = 073°; δ = +66° after 2h local time (β > 20° N)
IFC: α = 300°; δ = +40°; α = 000°; δ = +20° or
α = 240°; δ = +70° (β > 20° N)

The Perseids were one of the most exciting and dynamic meteor showers during the 1990s, with outbursts at a new primary maximum producing EZHRs of 400+ in 1991 and 1992. Rates from this peak decreased to ~ 100 —120 by the late 1990s, and in 2000, it first failed to appear. This was not unexpected, as the outbursts and the primary maximum (which was not noticed before 1988), were associated with the perihelion passage of the Perseids' parent comet 109P/Swift-Tuttle in 1992. The comet's orbital period is about 130 years, so it is now receding back into the outer Solar System, and theory predicts that such outburst rates should dwindle as the comet to Earth distance increases. However, some predictions suggested 2004 —2006 might bring a return of enhanced rates ahead of the usual maximum, and in 2004 a short, strong peak happened close to that anticipated pre-peak time. After that, activity seemed to be roughly normal in 2005, and the moonlit 2006 return was still to come when this text was prepared, but nothing untoward was predicted for 2007 in any case. An average annual shift of +0°05 in the λ of the “old” primary peak had been deduced from 1991 —99 data, and allowing for this could give a possible recurrence time around 9h UT on August 13 (λ = 140°16), if so a little after the most probable maximum, that of the “traditional” peak always previously found, which is given above. Another feature, seen only in IMO data from 1997 —99, was a tertiary peak at λ = 140°4, the repeat time for which would be 15h UT on August 13. Observers should be aware that these predictions may not be an absolute guide to the best from the Perseids, and plan their efforts accordingly, so as not to miss out, just in case!

Whatever happens, and whenever the peak or peaks fall around August 13, new Moon on August 12 creates perfect observing circumstances this year. For mid-northern latitudes, the radiant is sensibly observable from 22h —23h local time onwards, gaining altitude throughout the night. The UT morning-hour maxima suggested here would be best-viewed from across North America and northern South America, while the possible ~ 15h UT peak would fall best for Far Eastern Asia.

不管会发生什么,也不管8月13日附近会出现的是单个峰值还是多个峰值,8月12日的正值新月将创造出今年最佳的观测条件.对于北半球中纬度的地区,辐射点在22-23点的时候可以很明显的察觉到,高纬度的地区则整夜都行.这里提到的世界时早晨的最大峰值的最佳观测点在北美和南美的北部.另外一个可能出现的峰值(世界时15时,北京时23时)将对东亚有利.

Visual and still-imaging observers should need little encouragement to cover this stream, but telescopic and video watching near the main peak would be valuable in confirming or clarifying the possibly multiple nature of the Perseid radiant, something not detectable visually. Recent video results have shown a very simple, single radiant structure certainly. Radio data would naturally enable early confirmation, or detection, of perhaps otherwise unobserved maxima, assuming more than one takes place, if the timings or weather conditions prove unsuitable for land-based sites. The only negative aspect to the shower is the impossibility of covering it from the bulk of the southern hemisphere.

传统的目视和固定摄影方式观测并不是最值得鼓励的手段,值得鼓励的是在峰值附近的望远镜监测或者视频监测,这些手段可以用来论证或者澄清叠加在一起的多个英仙座流星辐射点(不知道是否理解错,我的理解是,因为一个辐射点往往由彗星一次回归的喷射物质形成,当地球同时遭遇2-3次回归彗星喷发的不同时期的流行体集团时,会导致多个辐射点的产生),这点是目视观测无法做到的.无心电观测同样可以作早期论证或者侦测到没有被发觉的峰值(这里假设确实出现了多个高峰),如果对于陆地观测点,极大时间落在白天或者天气状况一塌糊涂,无线电监测同样有效.唯一不好的地方是,对于南半球的大部分人来说,英仙座流星雨无法被观测到.

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