Electronic Telegram No. 773
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
CBAT@CFA.HARVARD.EDU (science)
URL http://cfa-www.harvard.edu/iau/cbat.html


GEMINID AND URSID METEORS 2006
       P. Jenniskens, SETI Institute, reports that the Geminid meteors from
(3200) Phaethon should peak at ZHR = 130 +/- 20 meteors/hr on 2006 Dec.
14d08h48m UT, with a FWHM of 26 hr (Jenniskens 2006, Meteor Showers and
Their Parent Comets, Cambridge Univ. Press, p. 397).  A waning 31-percent
crecent moon will not interfere before 1 a.m. local time.  Meteors should
radiate from a geocentric radiant of R.A. = 113.8 deg, Decl. = +32.4 deg
(equinox 2000.0), with velocities of V_g = 34.6 km/s.  On average, Geminids
are fainter in the days leading up to the peak than they are following the
peak; at its peak, the magnitude-distribution index (cf. CBET 710) is
predicted to be chi = 2.7.
     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).


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2006 CBAT
2006 December 12                 (CBET 773)               Daniel W. E. Green