Central Bureau for Astronomical Telegrams
IAUC 6329: C/1996 B2
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Circular No. 6329
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
BMARSDEN@CFA.HARVARD.EDU or DGREEN@CFA.HARVARD.EDU (science)
Phone 617-495-7244/7440/7444 (for emergency use only)
COMET C/1996 B2 (HYAKUTAKE)
In adopting, originally on IAUC 6304, the magnitude formula
(5.5 + 5 log Delta + 10 log r) for this comet, we were well aware that CCD
observations were then running up to 2 mag fainter and visual estimates up
to 1 mag brighter than this. This is still the case (see MPC 26606-26608,
IAUC 6328), which mainly serves to confirm that the choice of the term
10 log r (r**-4 variation) was not unreasonable. The following general
orbit, from MPC 26724 and utilizing observations through Feb. 27, shows
a 5-sigma departure from a parabolic solution, some worry about this
determination arising from the use of the isolated Jan. 1 prediscovery
observations:
Epoch = 1996 Apr. 27.0 TT
T = 1996 May 1.4025 TT Peri. = 130.1925
e = 0.999846 Node = 188.0514 2000.0
q = 0.230123 AU Incl. = 124.9016
Nevertheless, the adjustment necessary to obtain the "original"
barycentric orbit is quite large for this comet. The indications are thus
that this is NOT a "new" comet in the Oort sense, and that it was last
near the sun 10 000-20 000 years ago. This may inspire further confidence
in the r**-4 law, and since visual observations would seem more relevant
than CCD observations in discussions of naked-eye visibility, one might
expect the comet to become even brighter than predicted. It is important
to note, however, that when the comet is closest to the earth (0.102 AU
on Mar. 25.3 UT), that brightness is likely to be diffused over an area
several degrees across. More typical tail development is likely to
come later as the comet approaches the sun. The comet is unique in its
close passage to the earth and subsequent small perihelion distance.
If the brightness holds, it will be the intrinsically brightest comet
to pass so close to the earth since 1556. The ephemeris uncertainty is
still at least 1'.
1996 TT R. A. (2000) Decl. Delta r Elong. Phase m1
Mar. 13 14 55.36 -16 20.4 0.422 1.290 126.6 38.2 4.7
14 14 55.40 -15 10.7 0.389 1.271 127.9 38.1 4.5
15 14 55.38 -13 48.0 0.357 1.251 129.2 38.0 4.2
16 14 55.26 -12 08.8 0.325 1.232 130.6 37.8 4.0
17 14 55.04 -10 07.9 0.294 1.212 132.1 37.5 3.7
18 14 54.69 - 7 38.0 0.263 1.192 133.6 37.2 3.4
19 14 54.16 - 4 28.2 0.232 1.172 135.1 36.9 3.0
20 14 53.38 - 0 22.4 0.203 1.152 136.4 36.6 2.7
(C) Copyright 1996 CBAT
1996 February 29 (6329) Brian G. Marsden
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