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Past, Present, and Future Orbits by Kazuo Kinoshita

A. Nakamura image of 64P exposed on 2001 February 26
Copyright © 2000 by Akimasa Nakamura (Kuma Kogen Astronomical Observatory, Japan)

This CCD image was taken on 2001 February 26.70, using a 0.60-m f/6 Ritchey-Chretien telescope.


     L. Swift (Warner Observatory, Rochester, New York, USA) was engaged in the search for nebulae when he found an object of cometary appearance on 1889 November 17.13. It was located very close to Xi Pegasi and was described as "Pretty faint, large, little elongated." Swift said no motion was detected during the next 30 minutes and he suspected it was one of two nebulae that W. Herschel discovered near this star late in the 18th century, although Swift's position did not agree. He reobserved the object on November 17.99 and noticed it had moved, whereupon he sent a discovery announcement.
     Tom Gehrels (Palomar Mountain Observatory, California, USA) discovered this comet on a plate exposed with the 122-cm Schmidt telescope on 1973 February 8.29. He estimated the magnitude as 19, and described the comet as diffuse and 30 arc seconds across, with a sharp condensation, but no tail. Gehrels confirmed the discovery on February 9.30.

Historical Highlights

  • During the 1889-1890 discovery apparition, the comet was initially found about a month passed its closest distance from Earth and about two weeks before perihelion. During the remainder of November, observers generally described the comet as faint, with a gradual brightening toward the middle. The coma was 3-4 arc minutes across. The comet faded during December and the coma diameter decreased to 2 arc minutes across. The comet was last seen on 1890 January 22.24.
  • The first parabolic orbit was calculated by K. Zelbr using positions from November 17, 20, and 22. He determined the perihelion date as 1889 December 11.03. The first elliptical orbit was calculated by Zelbr using positions spanning the period of November 19 to December 9. He determined the perihelion date as November 30.13 and the period as 6.91 years. In the years following the comet's departure, J. R. Hind (1891) and J. Coniel (1896) calculated periods of 8.53 years and 8.92 years, respectively. Coniel commented that the uncertainty in the period was ±0.9 years, which would make it impracticable to provide ephemerides for the next return. After a second periodic comet was found by Swift in 1895, this comet officially became known as "Swift 1".
  • Following the comet's rediscovery in 1973, B. G. Marsden was able to publish an orbit on February 16. He said the comet was "probably of short period, for a parabolic solution indicates that there would have been a good chance of finding the comet last August." He assumed an eccentricity of 0.56, and obtained a perihelion date of August 1972, with a perihelion distance of 1.51 AU, and an inclination of 9°. Using 6 positions, Marsden computed a more precise elliptical orbit which was first published on February 28. The perihelion date was determined as 1972 August 29.77 and the orbital period was 8.43 years. Marsden noted a similarity between this orbit and that computed for the lost periodic comet Swift 1. He used 22 observations of Swift 1, which were obtained during 1889-1890, and redetermined the orbit. He then applied perturbations by Jupiter to Pluto and integrated the orbit up to 1973. The result was a perihelion date of August 30.25 and an orbital period of 8.38 years. Further positions enabled Marsden to revise the perihelion date to August 31.09 and the period to 9.23 years. Marsden said the comet passed close to Jupiter in 1910 (0.7 AU) and 1924 (1.0 AU), and that the comet would have had favorable perihelion passages in September 1935 and December 1944, which would have resulted in a maximum brightness of 14-15.
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