Electronic Telegram No. 1159
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://www.cfa.harvard.edu/iau/cbat.html


URSID METEORS 2007
     P. Jenniskens, SETI Institute, writes that he and his colleagues E.
Lyytinen, M. Nissinen, I. Yrjola, and J. Vaubaillon (Jennniskens et al.
2007, JIMO 35, Dec. issue, in press) predict an outburst of Ursid meteors
associated with the imminent return of comet 8P/Tuttle to perihelion.  The
peak of the outburst is predicted at 20-22.2 hr UT on Dec. 22 (most likely
21h.4-22h.2), when the shower rate (ZHR) will be about 40-80 meteors/hr, or
4-8 times the normal Ursid activity.  The outburst may last as short as FWHM
= 2 hr if dominated by dust trails that were ejected during AD 700-900, or
as long as FWHM = 8.5 hr if older dust trails are involved.  Meteors should
radiate from a geocentric radiant of R.A. = 218.3 deg, Decl. = +75.5 deg
(equinox 2000.0), with velocities of V_g = 33.52 km/s.  These results were
derived by calculating the orbital evolution of meteoroids ejected by
comet 8P in the period AD 300-1400; it was found that encounters with
Jupiter at the ascending node of the comet orbit shortly after ejection
move the meteoroids in mean-motion resonances that evolve the dust into
earth-crossing orbits, creating a stream or filament that is elongated
perpendicular to the earth's path.


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      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2007 CBAT
2007 December 10                 (CBET 1159)              Daniel W. E. Green