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Past, Present, and Future Orbits by Kazuo Kinoshita

Tim Puckett image of 45P exposed on 2011 September 29
Copyright © 2011 by Michael Jäger (Austria)

This image was taken by M. Jäger on 2011 September 29.14, using a 20-cm telescope, a Sigma 6303 CCD camera, and RGB filters. Three 4-minute exposures using an L filter, as well as 3-minute exposures using R, G, and B filters were all combined to produced this color image.


Periodic comet 45P/Honda-Mrkos-Pajdusakova is classed as a middle-age, dwarf comet, with a nucleus roughly 0.9 kilometers (0.5 mile) across. It belongs to the Jupiter family of comets (comets with periods less than 20 years). The comet was discovered in 1948. Although it then had an orbital period of 5.2 years, an analysis of its orbit reveals the period had been 5.5 years in 1933. A close approach to Jupiter in August 1935 (0.08 AU) reduced the period to 5.3 years. This is the comet's eleventh observed return since its discovery, having been missed in 1959 and 1985. The 2011 return is exceptional, as the comet will pass 0.06 AU from Earth on August 15.


     The comet was discovered by Minuru Honda on 1948 December 3, during a routine search for comets. He confirmed his discovery on December 5 and described the comet as diffuse with a magnitude of 9. The orbit was recognised as elliptical with period a little over 5 years by 1949 January.

Historical Highlights

  • The first parabolic orbit was calculated by L. E. Cunningham using positions obtained up to December 9. He determined the perihelion date as 1948 November 20.40. The first elliptical orbit was calculated by A. Schmitt, using positions from December 8, 11, and 14. The result was a perihelion date of November 18.49 and a period of 7.10 years. Schmitt noted, "The elements present a certain similarity to Biela's comet." Additional elliptical orbits were calculated by Schmitt, Cunningham, and G. Merton. These indicated a perihelion date of November 17.7–17.8 and a period of 5.00–5.31 years. Following observations at later apparitions, the perihelion date proved to have been November 17.72 and the period was 5.22 years. The comet passed 0.08 AU from Jupiter on 1935 August 15, at which time it was put into its discovery orbit.
  • The appearance of 1974-1975 was the comet's best return since it had been discovered. It had passed perihelion on 1974 December 28 and then passed closest to Earth on 1975 February 4 (0.2344 AU). The result was that it reached a maximum magnitude of 7.5 in January.
  • The comet's best appearance to date came during the apparition of 1995-1996. This was the comet's 8th appearance since its discovery. It had passed closest to the sun on 1995 December 25 (0.5319 AU) and passed closest to Earth on 1996 February 6 (0.1702 AU). During the last few days of December the total magnitude was estimated as around 6.5. The comet entered the sun's glare thereafter, and passed only 4.3 degrees from the sun on January 15. It was photographed by the Solar and Heliospheric Observatory (SOHO) from January 9 to 18. The comet was about magnitude 7.5 when it emerged from the sun's glare in late January. The comet appeared to have faded rapidly during March. It had faded to magnitude 9 by the 11th and was just slightly brighter than 11 on the 16th.
  • 2011: This was expected to be one of the comet's finest apparitions, as it would be passing closest to Earth (0.06 AU) on August 15 and then closest to the sun on September 28. From the beginning of July, the comet steadily brightened. Visual observers were reporting magnitudes near 12 by the beginning of August and 8 by August 14, afterwhich the comet became lost in the sun's glare. This last observation was reported by W. Souza (Sao Paulo, Brazil), who was using 20x80 binoculars. Most observers continually noted a small coma of 1' to 3' throughout this period, although J. J. Gonzalez (Leon, Spain) reported a coma diameter of 5' on July 28, 6' on August 1, and 8' on August 4 and 8, all using a 20-cm reflector. In addition, M. Goiato (Aracatuba, Brazil) reported a coma 12' across on August 11, using a 22-cm reflector. The comet reappeared in the morning sky on September 24.5, when E. Guido, G. Sostero, and N. Howes imaged the comet using a 25-cm reflector and a CCD camera at the remote GRAS Observatory (Mayhill, New Mexico, USA). They noted assymmetry in the coma toward the north-northeast. Three visual observers spotted the comet the next morning. J. Cerny (Czech Republic) observed the comet on September 25.11, using a 35-cm reflector. He gave the magnitude as 6.9 and noted a moderately condensed coma 3' across. There was also a tail extending 20' in PA 320 degrees. P. Guzik (Poland) spotted the comet on September 25.12, using 10x50 binoculars. He gave the magnitude as 6.7 and noted a strongly condensed coma 4' across. Gonzalez saw it on September 25.18 using 10x50 binoculars. He gave the magnitude as 6.6 and noted a moderately condensed coma 5' across. His 20-cm reflector revealed a tail extending 0.6 degree in PA 280 degrees.
  • Close approaches to planets: This comet made 11 close approaches to Earth and 2 close approaches to Jupiter during the 20th century. It makes 1 close approach to Venus, 5 close approaches to Earth, and 1 close approach to Jupiter during the first half of the 21st century. (From the orbital work of Kazuo Kinoshita)
    • 0.62 AU from Earth on 1900 July 31
    • 0.64 AU from Earth on 1906 March 20
    • 0.26 AU from Earth on 1917 January 16
    • 0.35 AU from Earth on 1927 November 24
    • 0.08 AU from Jupiter on 1935 August 15
      • decreased perihelion distance from 0.64 AU to 0.58 AU
      • decreased orbital period from 5.53 to 5.27 years
    • 0.83 AU from Earth on 1943 July 12
    • 0.43 AU from Earth on 1948 November 16 (contributed to comet's discovery)
    • 0.59 AU from Earth on 1954 March 15
    • 0.30 AU from Earth on 1969 August 11
    • 0.23 AU from Earth on 1975 February 5
    • 0.11 AU from Jupiter on 1983 March 26
      • decreased perihelion distance from 0.58 AU to 0.54 AU
      • increased orbital period from 5.28 to 5.30 years
    • 0.29 AU from Earth on 1990 August 1
    • 0.17 AU from Earth on 1996 February 4
    • 0.09 AU from Venus on 2006 June 4
    • 0.06 AU from Earth on 2011 August 15
    • 0.09 AU from Earth on 2017 February 11
    • 0.57 AU from Earth on 2027 July 20
    • 0.17 AU from Jupiter on 2030 August 3
      • increased perihelion distance from 0.56 AU to 0.63 AU
      • increased orbital period from 5.34 to 5.52 years
    • 0.37 AU from Earth on 2032 November 6
    • 0.39 AU from Earth on 2043 November 21

    Additional Images

    H. Mikuz image of 45P exposed on 1996 February 2
    Copyright © 1996 by Herman Mikuz (Crni Vhr Observatory, Slovenia)

    This V-filter image was taken on 1996 February 2 with the 20-cm, f/2 Baker-Schmidt camera and ST-6 CCD. Exposure time was 120s, starting at 4:49:40 UT. (The webmaster has reversed this image to better represent the comet's appearance.)

    Tim Puckett image of 45P exposed on 1995 December 28
    Copyright © 1995 by Tim Puckett

    This image was taken by Tim Puckett (Villa Rica, Georgia, USA) on 1995 December 28.99, using a 0.30-m f/7 Meade LX-200 and an SBIG ST-6 CCD camera. It is a 300-second exposure.

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