Central Bureau for Astronomical Telegrams
IAUC 3531: Obs OF COMETS
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Read IAUC 3532
Circular No. 3531
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
TWX 710-320-6842 ASTROGRAM CAM Telephone 617-864-5758
OBSERVATIONS OF COMETS
Further selected total visual magnitudes and coma diameters:
Periodic Comet Encke. Oct. 18.34 UT, 8.8, 10' (D. Machholz, San
Jose, CA, 0.25-m reflector); 20.36, 7.7, 12' (J. Bortle, Stormville,
NY, 10 x 50 binoculars); 21.39, 7.5, 12' (C. S. Morris,
Harvard, MA, 20 x 80 binoculars); 22.39, 7.4, 11' (Morris).
Periodic Comet Stephan-Oterma (1980g). Oct. 18.39 UT, 9.7, 4'
(Machholz); 20.37, 10.5, 2' (Bortle, 0.32-m reflector); 21.36,
9.8, 3' (Morris, 0.25-m reflector); 22.42, 10.1, 2' (Bortle).
Periodic Comet Tuttle (1980h). Oct. 18.46 UT, 8.9, 3'.5 (Machholz);
20.43, 9.2, 3' (Machholz); 22.39, 9.7, 2'.5 (Bortle).
Attention is drawn to the extremely precarious situation
concerning astrometric observations of comets. The situation has
noticeably deteriorated since 1978 Aug., when we ceased to publish
other than discovery (or recovery) and immediate-post-discovery
observations on these Circulars. Subsequent observations are more
efficiently published in the MPCs ("Minor Planet Clrculars"/"Minor
Planets and Comets"), also issued by the Smithsonian Astrophysical
Observatory. This does not mean that accurate positional observations
of comets are no longer of value, and observers are urged to
communicate their results to the Central Bureau (or Minor Planet
Center) just as before; the MPCs are published only slightly less
rapidly than the IAUCs and are received by all interested users.
The seriousness of the situation is well illustrated by the three
short-period comets currently bright enough to be detected with
small telescopes (see above): this year we have received precisely
two usable observations of P/Encke (MPC 5485, IAUC 3526); apart from
the recovery observations (IAUC 3488, MPC 5439), there has been
precisely one usable observation of P/Stephan-Oterma (the first one on
MPC 5456); and apart from the recovery observations (IAUC 3493, MPC
5430), there has not been a single positional observation of
P/Tuttle. Many astronomers have been interested in making physical
observations of these comets, and the Central Bureau has received
numerous requests for updated orbital data. The predicted orbits
for these three comets were all rather good, but because the
nongravitational forces cannot be modeled exactly, it is desirable to
adjust the predictions using current observations; otherwise, no
satisfactory response can be made to those astronomers contemplating
radio, radar or ultraviolet observations of comets.
1980 October 31 (3531) Brian G. Marsden
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