June Boötids (JBO)
This source was reinstated on the Working List after its unexpected return of 1998, when ZHRs of 50–100+ were visible for more than half a day. Another outburst of similar length, but with ZHRs of ~ 20–50 was observed on 2004 June 23, a date before definite activity had previously been recorded from this shower. Consequently, the shower’s start date was altered to try to ensure future activity so early is caught, and we encourage all observers to routinely monitor throughout the proposed activity period, in case of fresh outbursts. Prior to 1998, only three more probable returns had been detected, in 1916, 1921 and 1927, and with no significant reports between 1928 and 1997, it seemed likely these meteoroids no longer encountered Earth. The dynamics of the stream were poorly understood, although recent theoretical modelling has improved our comprehension. The shower’s parent, Comet 7P/Pons-Winnecke, has an orbit that now lies around 0.24 astronomical units outside the Earth’s at its closest approach. Its most recent perihelion passage was in 2008 September. Clearly, the 1998 and 2004 returns resulted from material shed by the comet in the past which now lies on slightly different orbits to the comet itself. Dust trails laid down at various perihelion returns during the 19th century seem to have been responsible for the last two main outbursts. Four similar dust trails are predicted to encounter the Earth this year, laid down by the comet in 1819, 1825, 1830 and 1836, which may produce UT maxima around June 24, 03h53m,01h22m, 00h07m and June 23, 22h40m respectively. Activity is uncertain, but is not expected to be particularly high, so perhaps will be no better than at the 2004 return. Conditions for checking are very unfavourable from the mid-northern latitudes where the radiant is best-seen, with full Moon on June 26, aside from the prolonged – in some places continuous – twilight, but it is important to discover whether activity recurs at all, and if so when. The radiant is usefully accessible virtually all night, and all observing techniques can be employed. In terms of the apparently ‘early’ predicted peaks this time, VID suggested some June Boötids may be visible in most years around June 20–25, but that their activity was largely negligible except near λo = 92◦ (2010 June 23). Even stranger was that this activity originated from a radiant about ten degrees south of the visual one found in 1998 and 2004, close to α = 216◦, δ = +38◦.
牧夫座流星雨是由7P/庞斯-温尼克彗星抛射的尘埃物与地球相遇形成，由于流星物质的分布不是很均匀，当地球遇到彗星近日点附近抛射的较密集的尘埃团时，就会有增强活动，在1916, 1921 ，1927，1998，2004年观测到比较明显的活动，但是其间有近70年没有观测到明显的流星雨（也许这就是专家所说的70年一遇，哈哈），所以近似周期为5-6年，今年有可能出现活动，当然，这也只是推测，也有可能观测不到增强的活动，毕竟不像日月食那样可以精确预报，所以请爱好者进行监测，对牧夫座流星群的研究很有价值。 |
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置顶卡
变色卡
千斤顶
显身卡
