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75D/Kohoutek

Past, Present, and Future Orbits by Kazuo Kinoshita

Discovery

     Lubos Kohoutek (Hamburg Observatory, Germany) discovered this comet during late February 1975, on a plate exposed on February 9.77, 1975. He estimated the magnitude as 14 and described the comet as diffuse with a condensation. Unfortunately, the comet appeared on only one plate, so that the motion was ambiguous. On February 27, Kohoutek began to search for the comet to the southwest and northeast of the February 9 position. Coincidentally, he did find a comet to the southwest, but events during the next few days proved this was not the comet he was looking for, but, instead, another new one (see 76P/West-Kohoutek-Ikemura). During the first days of March, Kohoutek reexamined his search plates of February 27 and found a very faint 15th-magnitude cometary trail on a plate exposed northeast of the February 9 position. Upon announcing this find to the Central Bureau for Astronomical Telegrams, J. H. Bulgar (Harvard College Observatory, Agassiz station) photographed the comet with the 155-cm reflector on March 5, thus confirming Kohoutek's faint February 27 image and offering the definitive link to the object of February 9. Bulgar estimated the magnitude as 15.

Historical Highlights

  • The comet was followed until 1976 April 29, when Elizabeth Roemer estimated the nuclear magnitude as 21.5. Orbital computations revealed an orbital period of 6.23 years and a perihelion distance of 1.57 AU. The comet was moved into its discovery orbit when it passed 0.142 AU from Jupiter on July 28, 1972. Prior to this encounter the comet's orbital period was 8.50 years and the perihelion distance was 2.51 AU.
  • Following the 1975 apparition the comet was next expected at perihelion during 1981. It was recovered on 1980 August 6 at a position indicating the predictions were only -0.68 day off. This was not a particularly good apparition and the comet's maximum brightness only reached 18.
  • The comet's 1987 apparition was an exceptional one. The comet was recovered on 1986 July 30 by T. Gehrels and J. V. Scotti (Kitt Peak, Arizona, USA), with the brightness estimated as magnitude 19.5. The comet was then more than a year from its perihelion date of 1987 October 30. As the distances from both the sun and Earth decreased during the latter half of 1987 observers began consistently reporting the comet's magnitude as brighter than 14. Around the time the comet was closest to Earth on 1988 January 13 (0.9467 AU) most observers noted a magnitude around 13. The comet was last seen on 1988 May 19.
  • The comet was missed at the poor 1994 return, as well as its 2001 and 2007 returns. The comet's next three returns will fall in 2014, 2021, and 2027. A close approach to Jupiter in 2032 (0.29 AU) will bring a notable change to the orbit, decreasing the perihelion distance from 1.77 AU to 1.38 AU and the period from 6.64 years to 5.85 years.
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