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Past, Present, and Future Orbits by Kazuo Kinoshita

A. Nakamura image of 68P exposed on 1998 July 3
Copyright © 1998 by Akimasa Nakamura (Kuma Kogen Astronomical Observatory, Japan)

This CCD image was taken on 1998 July 3, using a 0.60-m f/6 Ritchey-Chretien telescope.


     While examining photographs exposed with the 20-inch double astrograph at the Yale-Columbia Southern Station in Argentina, Arnold R. Klemola found a moving object of magnitude 17. The first photograph had been exposed on 1965 October 28.07. Klemola described the comet as "slightly nebulous" with a diameter near 12 arc seconds. The additional photographs had been exposed on October 29.06, October 31.09, November 1.12, and November 2.02.

Historical Highlights

  • The initial images found by Klemola were enough to enable B. G. Marsden (Smithsonian Astrophysical Observatory) to compute a parabolic orbit which was first published on November 15. The perihelion date was determined as 1965 September 17.1. Following the acquisition of additional images, Marsden computed the first elliptical orbit just 8 days later. It indicated the perihelion date was August 25.3, while the orbital period was 18.8 years. After all of the observations had been accumulated, Marsden revised his elliptical orbit during 1967 and determined the perihelion date as August 18.4 and the period as 10.97 years. He suggested an uncertainty of two months in the period. Kaare Aksnes investigated the past motion of this comet and reported no significant change during the last 70 years.
  • The comet never exceeded magnitude 17 during the discovery apparition of 1965. It was last detected on December 13.
  • G. Sause (Observatoire Haute Provence) recovered this comet with the O.H.P.-Universite de Liege Schmidt telescope on 1976 August 6.07. He estimated the magnitude as 12 and said the tail was 2 or 3 arc minutes long. The position indicated the prediction that appeared in the 1976 edition of the British Astronomical Association Handbook required a correction of -10.2 days. The comet maintained a brightness near magnitude 12 during the remainder of August and for most of September. It faded thereafter and was last detected on 1977 January 21.
  • The comet's third observed apparition came in 1987 when J. Gibson (Palomar Observatory, California, USA) obtained CCD images with the 1.5-meter reflector on 1987 February 16.56. He said it was essentially stellar, with an estimated magnitude of 19. There was also a tail toward PA 210-270 degrees that was bordered by streamers about 15 arc seconds long. The position indicated the prediction required a correction of -0.01 day. The comet brightened and attained a maximum magnitude of about 12.5 during September. It was last detected on 1988 December 10.
  • The comet's fourth observed apparition began on 1997 March 29, when C. W. Hergenrother (F. L. Whipple Observatory) obtained CCD images of the comet with the 1.2-meter reflector. The comet was essentially stellar in appearance, with a magnitude of 21.4. The comet passed perihelion on 1998 May 1 and reached magnitude 14 during the summer months of 1998.
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