Kedves Lelkes Hullócsillagszeretők!

Jenniskens előrejelzése szerint kis szerencsével a ma/holnap (P/Sz) éjfél körüli
órákban Ursida-kitörésben lehet részünk. A vonatkozó szakirodalmat (az IAU által
kibocsátott CBET #773 erre vonatkozó részét alább beidézem, de előtte:

Ha már ilyen szépen kiderült, és a derült idő esélye (főleg magasabb helyeken)
nullánál nagyobb, feltenném a kérdést: ki jön ki velünk ursidázni? Indulás a
(nem túl) késő esti órákban, vélelmezhetően a Pilis esetleg a Mátra tetejére.

Üdv:
Tepi   (+36-20-922-5242)


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      Jenniskens adds that E. Lyytinen and M. Nissinen (Helsinki, Finland)
have identified an encounter of the earth with the 75-revolution dust trail
(dating back to 996 AD) of comet 8P/Tuttle around 2006 Dec. 22d19h27m UT,
with meteoroids in the earth´s path between 18h10m and 20h50m, depending on
the adopted value for nongravitational acceleration (this updates Jenniskens
2006, Meteor Showers and their Parent Comets, Cambridge Univ. Press, p. 641).
A 6-percent moon in Cap will not interfere.  Meteors should radiate from a
geocentric radiant of R.A. = 217.56 deg, Decl. = +74.93 deg (equinox 2000.0),
with velocities of V_g = 33.83 km/s.  Particles could be mostly faint with a
magnitude-distrubtion index of chi around 2.8.  A predicted peak rate of ZHR
around 35 meteors/hr would be about three times that of the annual Ursids.
The calculations assume that, back in 996 AD, 8P/Tuttle behaved much as it
does now.  The previous oldest trail traced into the earth´s path (in AD
2000) is dated to AD 1405.  The meteoroid orbits are not strongly perturbed
by Jupiter, so that the meteoroids tend to accumulate over time in a
component called a "filament" (such filaments are known from comets 109P,
55P, 1P, and 8P).  Jenniskens also points out that it is possible that a
broader (FWHM = 8.5 hr) filament dust component will return, peaking at
around 2006 Dec. 22d17h38m with ZHR around 39 meteors/hr and with chi = 2.6.
That filament was seen before 1982 and in 1993-1998, during previous returns
of the comet to perihelion.  The 1945 display was identified by Jenniskens
et al. (2002, Icarus 159, 197-209) as due to a more-or-less well-behaved
dust trailet ejected in 1392; the calculated peak time of the shower was
1945 Dec. 22d18h29m UT, close to the time of the observations.  Comet
8P/Tuttle is due back at perihelion on 2008 Jan. 26.9 TT (MPC 54167).