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THE ASTRONOMER Electronic Circular No 2288      2006 Dec 15 15.44UT
Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise,  Basingstoke,
Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074
INTERNET: GUY@TAHQ.DEMON.CO.UK      Backup: gmh@wdcc1.bnsc.rl.ac.uk
WORLD WIDE WEB                         http://www.theastronomer.org
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URSIDS 2006
E. Lyytinen and M. Nissinen, Finland have identified, according to CBET 
773, 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 non-gravitational acceleration.

Meteors should radiate from a geocentric radiant of R.A. = 217.56 deg, 
Decl. = +74.93 deg (2000), with velocities of V_g = 33.83 km/s. 
Particles could be mostly faint with a magnitude-distribution 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. 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).

Guy M Hurst