June Boοtids (JBO): 22 Ιουν. ως 2 Ιουλ. Μέγ: 27 Ιουν. 2011

πηγη IMO.net

June Boοtids (JBO)

Active: June 22 – July 2; Maximum: June 27, 21h UT (λ = 95.7°), but see text;

ZHR = variable, 0–100+;

Radiant: α = 224°, δ = +48°; Radiant drift: see Table 6;

V∞ = 18 km/s; r = 2.2;

TFC: α = 156°, δ = +64° and α = 289°, δ = +67° (β = 25°–60° N).

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. The predicted possible activity in 2010 was still to come when this text was prepared. 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. No predictions for activity are in-force for 2011, but conditions for checking are very favourable from the mid-northern latitudes where the radiant is best-seen (indeed it is usefully-observable almost all night from here), with only a waning crescent Moon on June 27. The prolonged – in some places continuous – twilight will cause difficulties, however. VID has suggested some June Boötids may be visible in most years around June 20–25, but with activity largely negligible except near λ⊙ = 92° (2011 June 24), radiating from an area about ten degrees south of the visual one found in 1998 and 2004, close to α α = 216°, δ = +38°.