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128P/Shoemaker-Holt 1

Past, Present, and Future Orbits by Kazuo Kinoshita

J. Scotti image of 128P exposed on 1996 September 1
Copyright © 1997 by James V. Scotti

This image was obtained on 1996 September 21 with the 0.91-m Spacewatch telescope. The comet, as well as its more diffuse companion, are near the center of the image. The field of view is 3.5 arc minutes square.


     The discovery of this comet was first announced on IAU Circular 4472 (1987 October 19). The comet was found by Carolyn S. Shoemaker, Eugene M. Shoemaker, and Henry E. Holt on plates obtained on 1987 October 18.3 and October 19.5 with the 0.46-m Schmidt telescope at Palomar Observatory. It was described as "strongly condensed, with a slight coma asymmetric toward the southwest." Its photographic magnitude was estimated as 14.5.

Historical Highlights

  • Daniel W. E. Green (Central Bureau for Astronomical Telegrams) published the first orbit on IAU Circular 4479 (1987 October 26). Using 7 positions obtained during the period of October 18 to 23, Green computed an elliptical orbit with an orbital period of 9.04 years. A revised orbit was later computed by Brian G. Marsden and was published on IAU Circular 4508 (1987 December 5). It indicated a perihelion date of 1988 May 21, a perihelion distance of 3.05 AU, and an orbital period of 9.6 years.
  • J. V. Scotti (University of Arizona, USA) recovered this comet with the Spacewatch telescope at Kitt Peak on 1996 September 19.19. His precise positions indicated the predicted perihelion date required a correction of -0.89 day, making the actual perihelion date 1997 November 20.25 (3.0470 AU). Scotti described the comet as between magnitude 20.7 and 21.1 at discovery. Interestingly, Scotti's images obtained on September 20 revealed a diffuse secondary companion situated about 4 arc seconds north-northeast of the main nucleus. The comet passed closest to Earth (2.06 AU) on November 27. The maximum magnitude was not expected to be much brighter than 15. Observations during 1997 December and 1998 January indicated the comet had reached magnitude 14.9. The coma diameter was about 0.8 arc minute.
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