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IAUC 5671: 1992t

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                                                  Circular No. 5671
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)


PERIODIC COMET SWIFT-TUTTLE (1992t)
     Further to IAUC 5670, Waddington, considering several assumed
values of A2 between -0.0075 and +0.0075, has independently shown that
A2 = -0.0025 yields T = +188 Aug. 17 and -68 July 15; although the
computation for -68 is heavily influenced by a close approach to the
earth in +188, this solution is significant in that it yields no
other approaches within 0.5 AU of the earth between +188 and 1737.
The general stability of Waddington's result is confirmed by G. V.
Williams (Harvard-Smithsonian Center for Astrophysics = CfA), who
finds that the actual orbit and similar nongravitational parameters
on IAUC 5670 yield T = +188 July 20 and an earth approach
to 0.23 AU 12 days later; with an arbitrary change of up to -20 days in
T a closer approach and a representation of the -68 observations becomes
possible.  J. E. Chambers (Manchester University and CfA) finds the
comet's long-term motion to be dominated by the 1:11 mean-motion
resonance with Jupiter, in spite of the nongravitational effects and
occasional encounters with the earth and Saturn.  Although post-perihelion
observations in 1993 and subsequently should be examined for a possible
repetition of the systematic residuals of 1862 Oct., the proposed
identity with the +188 comet suggests that the next two returns of
P/Swift-Tuttle will likely be within a day of T = 2126 July 11 and 2261
Aug. 12 and that there is very little possibility of the comet's
collision with the earth during the next millennium.

1992/93     R. A. (2000) Decl.     Delta      r    Elong. Phase      m1
Dec.  4    19 09.67    + 0 51.3    1.428    0.969   42.6   43.5      5.1
      6    19 15.08    - 1 08.7    1.462    0.964   40.9   42.0      5.1
      8    19 20.25    - 3 03.2    1.496    0.961   39.2   40.4      5.1
     10    19 25.20    - 4 52.6    1.530    0.959   37.5   38.7      5.2
     12    19 29.95    - 6 37.2    1.565    0.958   35.8   36.9      5.2
     14    19 34.51    - 8 17.1    1.600    0.959   34.1   35.1      5.2
     16    19 38.91    - 9 52.6    1.634    0.960   32.4   33.3      5.3
     18    19 43.17    -11 24.1    1.668    0.963   30.7   31.4      5.4

Feb. 12    21 24.70    -39 17.4    2.221    1.400   25.9   17.9      8.4
     17    21 34.65    -41 13.0    2.229    1.457   29.8   19.7      8.7
     22    21 45.06    -43 08.6    2.233    1.515   33.9   21.3      9.0
     27    21 56.01    -45 04.7    2.233    1.574   37.9   22.8      9.2
Mar.  4    22 07.58    -47 02.1    2.229    1.634   42.0   24.0      9.4


1992 December 5                (5671)              Brian G. Marsden

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