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138P/Shoemaker-Levy 7

Past, Present, and Future Orbits by Kazuo Kinoshita


     This comet was discovered by Carolyn S. and Eugene M. Shoemaker and David H. Levy on photographic plates exposed with the 0.46-m Schmidt telescope at Palomar Observatory (California, USA) on 1991 November 13. It was described as diffuse, with a condensation and was estimated as magnitude 16.5. An image on the 15th acted as an additional confirmation.

Historical Highlights

  • Daniel W. E. Green (Central Bureau for Astronomical Telegrams) computed the first orbit which was published on November 25. It was a parabolic orbit with a perihelion date of 1991 September 15, a perihelion distance of 1.23 AU, and an inclination of 10 degrees. He added, "This may be a short-period comet." This suggestion was confirmed by Green's colleague B. G. Marsden, who used additional positions obtained into December and published a short-period orbit on December 5. It indicated the perihelion date was October 27, the perihelion distance was 1.63 AU, and the orbital period was 6.72 years. Eventually the orbital period was refined to 6.73 years.
  • J. V. Scotti (Lunar and Planetary Laboratory, Arizona, USA) recovered this comet on CCD images obtained on 1998 July 25.43. The comet was described as magntiude 20.7 with a coma 6 arc seconds across. There was a tail extending 0.5 arc minute in PA 264 degrees. Precise positions indicated the prediction published by Marsden required a correction of -0.7 day.
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