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Past, Present, and Future Orbits by Kazuo Kinoshita

Giovanni Sostero photo of 77P/Longmore exposed on 2002 March 5
Copyright © 2002 by Giovanni Sostero (Italy)

This image was obtained by Giovanni Sostero and V. Gonano on 2002 March 5.03. It is a 300-second exposure obtained with a 0.3-m f/2.8 Schmidt-Schmidt, and a Hi-Sis 24 CCD camera. North is toward the top, while east is to the left.


     During the course of the Southern Sky Survey, Andrew Jonathan Longmore found this comet on a photographic plate obtained by P. R. Standen with the 1.22-m Schmidt telescope at Siding Spring Observatory (New South Wales, Australia) on 1975 June 10.63. The comet was described as diffuse, with some central condensation and a faint tail 15 arc seconds long. There was some initial confusion about the magnitude, but this was later confirmed as 17. Longmore photographically confirmed the discovery on June 11.58, with the 1.22-m Schmidt telescope, and he and P. Wallace visually confirmed it on June 11.67, with the 3.81-m reflector.

Historical Highlights

  • The first published orbit was a "necessarily uncertain" one from B. G. Marsden (Central Bureau for Astronomical Telegrams), which was published on August 5. Using three precise positions obtained between June 10 and July 9, Marsden computed an elliptical orbit with a perihelion date of 1974 November 2.83 and a period of 7.05 years. Marsden said the calculations "suggest that the comet made a close approach to Jupiter in 1963." With the comet so faint and located in the Southern Hemisphere, observations were not plentiful and a revised orbit was not calculated until October 3. At that time, Marsden determined the perihelion date as November 4.34 and the period as 6.98 years.
  • Only eight precise positions were obtained during he first apparition and the comet was last seen on October 4.08 and October 4.13, when V. M. and B. M. Blanco (Cerro Tololo Observatory) photographed the it with the 400-cm reflector. They estimated the nuclear magnitude as 19.0.
  • S. W. Milbourn published the prediction for the 1981 return in the BAA Handbook for 1980. Using all 8 positions from 1975, he applied perturbations by Venus to Neptune and determined the perihelion date as 1981 October 21.55. T. Seki (Geisei, Japan) recovered the comet on 1981 Jan. 2.80 and 3.78. He estimated the magnitude as 18 and described the comet as diffuse and condensed. The positions indicated Milbourn's orbit needed a correction of +0.23 day. As with the discovery apparition, observations were few and far between. Following additional precise positions at other observatories on January 8 and February 6, the next position was not obtained until June 6. The next and final positions were then obtained over a year later, on 1982 July 26.
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