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Past, Present, and Future Orbits by Kazuo Kinoshita


     Antonin Mrkos (Klet Observatory) reported the discovery of a fast-moving object to the Central Bureau for Astronomical Telegrams on 1991 March 17. The object had appeared on photographic plates exposed on March 16.96 and March 17.04, but it was not certain whether this was a minor planet or a comet. He estimated the magnitude as 15. Following the announcement, Mrkos confirmed his find on March 17.98 and March 18.03, but noted the object was diffuse, with a central condensation, thus, establishing the cometary nature. The magnitude was again estimated as 15. Before Mrkos' confirmation had arrived, astronomers at Palomar Observatory in California independently confirmed the object with the 0.46-m Schmidt telescope. They also also noted it was somewhat diffuse, and gave the total magnitude as 14.0.
     Prediscovery images were announced by Y. Kushida and O. Muramatsu (Yatsugatake South Base Observatory). They found images of the comet on plates exposed on March 16.74 and March 17.60, and estimated the magnitude as 14.

Historical Highlights

  • As noted above, Mrkos did not initially recognise the object was a comet. Interestingly, on March 20, 1991, R. H. McNaught reported the comet was extremely condensed with a very small coma, and on March 21, Alan Hale reported the comet appeared like a star with some diffuseness. The comet reached a maximum magnitude of between 13.8 and 14.0 during its 1991 appearance.
  • The comet's recovery was announced during 1995 October. C. W. Hergenrother (Lunar and Planetary Laboratory, Arizona, USA) found the comet on CCD images obtained by S. Larson on September 20.42. The nuclear magnitude (red light) was then between 21.7 and 22.3. Meanwhile, W. Offutt (Cloudcroft, New Mexico, USA) had independently obtained very poor CCD images of the comet on September 28.37. It wasn't until October 21.22, that Offutt could confirm the recovery. The total magnitude was then determined as between 19.1 and 20.6. The comet reached its most northerly declination of +45.5° in mid-May 1996. It was then situated within 20° of the sun from early July until early October 1996. The comet passed perihelion on November 9 (1.413 AU) and was then closest to Earth on 1997 June 16 (1.7968 AU).
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