June Boötids (JBO)
Active: June 26 —July 2; Maximum: June 27, 14h00m UT (λ = 95°7);
ZHR = variable, 0 —100+;
Radiant: α = 224°, δ = +47°; Radiant drift: see Table 6 (page 23);
v∞ = 14 km/s; r = 2.2;
TFC: α = 156°, δ = +64° and α = 289°, δ = +67° (β = 25° —60° N).
Following its unexpected return of 1998, when ZHRs of 50 —100+ were visible for more than half a day, this source was reinstated on the Working List of Visual Meteor Showers. A further 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. We encourage all observers to routinely monitor the expected activity period at least in case of future outbursts. Prior to 1998, only three definite returns had been detected, in 1916, 1921 and 1927, and with no significant reports between 1928 —1997, it seemed probable 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. Consequently, the 1998 and 2004 returns resulted from material shed by the comet in the past, and 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. There are no predictions in force for possible activity in 2006 as yet, but new Moon on June 25 means if anything does occur during the shower's possible active period, conditions will be ideal for all forms of observation. At mid-northern sites, the radiant is at a useful elevation for most of the short summer nights, so please be alert! |
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置顶卡
变色卡
千斤顶
显身卡
