Central Bureau for Astronomical Telegrams
IAUC 5839: PERSEID METEORS
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Circular No. 5839
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM EASYLINK 62794505
MARSDEN@CFA or GREEN@CFA (.SPAN, .BITNET or .HARVARD.EDU)
PERSEID METEORS
Following the impressive Perseid activity in 1991 and 1992, with
hourly rates of a few hundred for about 1 hour near the time t_0
when the earth was crossing the orbit plane of P/Swift-Tuttle (IAUC
5330, 5386), and the subsequent recovery of the comet (IAUC 5620),
there has been widespread speculation on the possibility of even a
storm of Perseids (e.g., Rao 1993, Sky Tel. 86, No. 2, 43) around
t_0 = 1993 Aug. 12.05 UT, some 7.5 months after the comet was at its
descending node. Although records of both the comet (IAUC 5670)
and the Perseids have been traced back for 2000 years, there is no
record of a Perseid shower prior to the nineteenth century within
several years of a passage of the comet through this node. There
was impressive Perseid activity during 1861-1863, a dynamical difference
then being that the distance between the node and the earth's orbit,
0.005 AU, was significantly less than the 0.01-0.03 AU at the comet's
previous nodal passages (Marsden et al. 1993, Icarus, submitted). It is
the present even smaller distance, 0.0009 AU, coupled with the
circumstantial evidence that meteor storms tend to follow their parent
comets (cf. the Leonids; e.g., Yeomans 1981, Icarus 47, 492), that has
led to the current interest. On the assumption that the 1991 and 1992
events were produced by the ejection of material from P/Swift-Tuttle
in 1862, I. P. Williams and Z. Wu, Queen Mary and Westfield College,
London, calculate that the maximum activity in 1993 could be at any
time between Aug. 11.92 and 12.06 UT, and that there is more
likelihood of an actual Perseid storm in 1994. L. Kresak,
Astronomical Institute, Bratislava, indicates that any real storm in
1993 would be likely to occur close to t_0. In any case, comparison
with 1863 (Olson and Doescher 1993, Sky Tel. 86, No. 2, 47), when t_0
= 1863 Aug. 10.68 UT occurred some 11 months after the comet passed
its node, suggests the potential for impressive Perseid activity up
to fully 0.7 day after t_0.
R. Stachnik, NASA Headquarters, draws attention to the possibility
of observing sunlight scattered from meteoritic dust in the general
direction of the Perseid radiant and anti-radiant. Rao (loc. cit.)
indicates that the points to observe are roughly 10 deg south of Algol
and in Triangulum Australe. J. G. Hills and C. Snell, Los Alamos
National Laboratory, remark that, if the earth experiences a meteor
storm, many meteoroids would hit the moon about 0.15 day earlier.
They suggest that there is a non-negligible probability of impact by
1-m meteoroids, which with densities of 0.2 g cm-3 and impact velocity
60 km/s could produce observable flashes of duration 1 second to mag 1
on the dark portion of the last-quarter moon.
1993 August 5 (5839) Brian G. Marsden
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