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100P/Hartley 1

Past, Present, and Future Orbits by Kazuo Kinoshita

A. Nakamura image of 100P exposed on 1997 March 5
Copyright © 1997 by Akimasa Nakamura (Kuma Kogen Astronomical Observatory, Japan)

This CCD image was taken on 1997 March 5.71, using a 0.60-m f/6 Ritchey-Chretien telescope.


     Malcolm Hartley (U.K. Schmidt Telescope Unit, Australia) discovered this comet on a pair of plates exposed with a 1.2-m Schmidt on 1985 June 13.38 and June 13.48. He estimated the magnitude as 16 and said there was a prominent tail extending over one arc minute toward the southeast.

Historical Highlights

  • Following Hartley's acquisition of a photo of the comet on July 10, Brian G. Marsden was able to compute an elliptical orbit which he first published on July 18. This revealed a perihelion date of 1985 June 11, a perihelion distance of 1.54 AU, and an orbital period of 5.66 years.
  • During the first apparition, the comet was only kept under observation until August 14, or for barely two months. Subsequently, there was some uncertainty in the orbit. Using the available positions, S. Nakano predicted the comet would next arrive at perihelion on 1991 April 28.75.
  • The comet might have become lost if it was not for the accidental recovery by Carolyn and Eugene Shoemaker and David Levy in 1991. Using the 0.46-m Schmidt at Palomar Observatory, the team announced the discovery of a comet on a pair of plates exposed on 1991 March 12. They described it as magnitude 16.5, diffuse and condensed, with a tail extending over one arc minute. Brian G. Marsden (Harvard-Smithsonian Center for Astrophysics) noted the comet was about 16 degrees from the prediction for periodic comet Hartley 1 and was moving similar to what would be expected for that comet. He then computed an orbit that successfully linked the 1985 and 1991 positions, noting that Hartley 1 had passed 0.36 AU from Jupiter during 1988 February. Marsden showed that the comet's perihelion date in 1991 was May 17.68.
  • The comet attained a maximum magnitude of 14 during the 1991 apparition, 14.5 during the 1997 apparition, and 18 during the 2003 apparition.
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