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61P/Shajn-Schaldach

Past, Present, and Future Orbits by Kazuo Kinoshita

A. Nakamura image of 61P exposed on 2000 July 26
Copyright © 2000 by Akimasa Nakamura (Kuma Kogen Astronomical Observatory, Japan)

This CCD image was taken on 2000 July 26.62, using a 0.60-m f/6 Ritchey-Chretien telescope.

Discovery

     This comet was discovered by Pelageja F. Shajn (Crimean Astrophysical Observatory, Simeis) on a routine minor planet plate exposed with the 12-cm Maltsev double astrograph on 1949 September 18.9. An independent discovery was made by Robert D. Schaldach (Lowell Observatory, Arizona, USA) on September 20.3, while examining a routine minor planet plate exposed with the 33-cm Cooke triplet. Shajn later found prediscovery images of the comet on plates exposed on August 28 and September 4.

Historical Highlights

  • The first orbit was calculated by A. D. Maxwell. Using positions covering the period spanning September 20 to 27, he gave a parabolic orbit with a perihelion date of 1950 October 22.67. The first elliptical orbit was published on October 6, and was by Amelia White. She took three positions covering the period of September 20 to 28 and determined the perihelion date as 1949 December 7.68 and the period as 7.76 years. Leland E. Cunningham added that the comet probably approached to within 0.5 AU of Jupiter during 1947 "and it is likely the orbit was altered considerably." Alexander D. Dubiago computed a definitive orbit for the 1949 apparition.
  • J. T. Foxell used Dubiago's orbit for the 1949 apparition and computed perturbations up to 1957. The final result was his prediction that the comet would next reach perihelion on 1957 March 15.31. Observers at Lick Observatory (California, USA) photographed the predicted position of this comet on 1956 April 17 and May 17. H. M. Jeffers said the comet was not found and concluded it was then fainter than magnitude 18 and/or more than 20 arc minutes from the predicted positions. Attempts to find the comet at the 1964 apparition were also unsuccessful.
  • B. G. Marsden redetermined the orbit of this comet during 1970. Using the available precise positions obtained during 1949, and applying perturbations by all nine planets, he determined a perihelion date of 1971 October 4.45. Marsden said the uncertainty in the date of perihelion was ±5 days. He added, "the failure to recover the comet at its 1957 and 1964 returns is clearly due to its having been fainter than predicted."
  • Charles T. Kowal (Department of Astrophysics, California Institute of Technology, USA) recovered this comet with the 122-cm Palomar Schmidt on 1971 September 29.38. He estimated the magnitude as 16 and described the comet as well condensed, with a short tail due west. Kowal confirmed the recovery on September 30.43. The positions indicated Marsden's prediction needed a correction of -2.5 days. Several pre-recovery images were also found. During January 1972, A. C. Danks (Institut d'Astrophysique, Université de Liège) reported pre-recovery images had been found. Danks and M. G. Sause had exposed the plates with the 60-cm Liège Schmidt at Haute Provence on September 15.06, September 16.13, September 18.02, and September 18.11. On each of the plates the comet appeared as somewhat diffuse, with a trace of tail. During early 1973, C. Torres (Department of Astronomy, University of Chile) found an image of the comet on a plate exposed on September 16.31. He described it as a small, diffuse spot.
  • Magnitude estimates during 1971 were typically between 16.2 and 16.5 during October and November, while the coma was about 1 arc minute across. The comet was observed at its returns in 1979, 1986, 1993, 2001, and 2008.
  • Close approaches to planets: The comet experienced three close approaches to Jupiter since 1946. It will make only one minor approach to Jupiter during the next 50 years.
    • 0.18 AU from Jupiter on 1946 April 28
      • decreased perihelion distance from 4.30 AU to 2.23 AU
      • decreased orbital period from 10.60 to 7.27 years
    • 1.68 AU from Jupiter on 1981 July 17
      • increased perihelion distance from 2.22 AU to 2.33 AU
      • increased orbital period from 7.25 to 7.46 years
    • 1.04 AU from Jupiter on 2006 January 15
      • decreased perihelion distance from 2.33 AU to 2.11 AU
      • decreased orbital period from 7.46 to 7.05 years
    • 1.45 AU from Jupiter on 2041 July 22
      • decreased perihelion distance from 2.12 AU to 2.00 AU
      • decreased orbital period from 7.08 to 6.86 years

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