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73P/Schwassmann-Wachmann 3

Past, Present, and Future Orbits by Kazuo Kinoshita

Mike F. Holloway image of 73P exposed on 2006 April 27
Copyright © 2006 by Mike F. Holloway (Holloway Comet Observatory, Van Buren, Arkansas, USA)

This image was taken on 2006 April 27 by Mike F. Holloway. It was taken with a 4-inch f/5.3 FSQ refractor and an FLI Maxcam 10 CCD camera. It is composed of three 40-second exposures. The field of view is about 1 x 1.5 degree, with north at the top and east to the left. The image shows fragments "B", the bright comet on the left side, and "G", the faint comet on the right side.


     Friedrich Carl Arnold Schwassmann and Arno Arthur Wachmann (Hamburg Observatory, Bergedorf, Germany) discovered this comet on photographs exposed for a minor planet survey on 1930 May 2. The comet was then described as diffuse and magnitude 9.5. A few days later, H. Schneller (Berlin-Babelsberg Observatory, Germany) found prediscovery images on photographic plates exposed on April 27 and 29.

Historical Highlights

  • The comet reached a maximum brightness of between 6 and 7 during its discovery apparition when it passed only 0.0616 AU from Earth on 1930 May 31.
  • The comet was last seen on 1930 August 24. The existing observations allowed the determination of a short-period orbit, with astronomers giving periods ranging from 5.43 to 5.46 years.
  • The comet is intrinsically faint and, when combined with the slight variation in the computed orbital period and a very unfavorable apparition at its first predicted return in 1935-1936, it became lost after the 1930 appearance. Searches during the next several apparitions failed to locate the comet. Further complicating things was an approach to within 0.9 AU of Jupiter during 1953 October and 0.25 AU in 1965 November.
  • Revised orbital computations by Belyaev and Shaporev in 1973 led to the recognition that although the apparition of 1974 would be very unfavorable, the comet's return in 1979 would be the most favorable since 1930.
    [Perihelion Date=1979 September 2.78; Period=5.36 years]
    J. Johnston and M. Buhagiar (Perth Observatory, Australia) reported the discovery of a comet on plates exposed during a minor planet survey on 1979 August 13. Confirmation was made on August 15, and M. P. Candy (Perth Observatory) noted the comet's direction and rate of motion resembled what was expected for the lost comet Schwassmann-Wachmann 3. This was confirmed and the comet's perihelion date was found to be 34 days later than predicted. The comet attained a maximum magnitude of 12.5 around the time it passed closest to Earth (1.4359 AU) on March 19.

    [Perihelion Date=1990 May 19.30; Period=5.35 years]
    The comet was missed during the 1985-86 apparition, but was observed in 1990. This was the best appearance since 1930. On April 17, the comet passed 0.3661 AU from Earth and reached a maximum magnitude of 9.

    [Perihelion Date=1995 September 22.89; Period=5.34 years]
    [Images] This appearance was not supposed to be a very good one with the comet's closest approach to Earth on 1995 October 17 (1.3114 AU) being nearly 1 AU further than the exceptional 1990 apparition. The comet was meeting the expectations of astronomers when it was seen by K. Kinoshita (Japan) on August 19 at magnitude 12.9, but then something happened. Astronomers using the Nancay Radio Telescope were monitoring the comet's emissions during early September, just after the comet's minimum elongation from the sun on August 31 (40 degrees), when they detected an increase in OH on September 8. The emissions continued to increase through the 13th. By the 17th, the comet had moved far enough out of the sun's glare to enable visual observations and the brightness was found to be magnitude 8.3. That brightness more or less held until the beginning of October, when several observers reported it had increased to magnitude 6. Although the comet was still in twilight and at a low altitude, it was then visible in binoculars as a slightly diffuse star. The comet faded slightly thereafter and then underwent a third outburst back to 6.3 on October 22. The comet faded very slowly after its last outburst. Although it was then moving away from both the sun and Earth, observers continued reporting the total magnitude as 7.5 to 8 through the end of November and 8 to 8.5 through the first two-thirds of December. The comet became more diffuse during the remainder of December and into January and a rapid fading finally set in during the latter month. By February the brightness had dropped back to magnitude 14. Another surprise came in December when observatories began reporting mulitple nuclei within the coma of the comet. Four nuclei were officially designated and were labeled "A", "B", "C", and "D"; however, "D" was not observed elsewhere and may have been a very short-lived condensation. Three additional condensations were reported, but not designated, because they were also not seen elsewhere. Component "A" was discovered on 1995 December 23 and was last detected on 1996 February 19. Component "B" was discovered on 1995 December 23 and was last detected on 1996 December 14. Component "C" turns out to be the main body of the comet and was followed until 1996 December 14. It is interesting to note that Z. Sekanina published an article in the International Comet Quarterly (2005) that offers an excellent argument that the observations attributed to component "B" during 1996 may actually belong to two different components. He suggests "B" was seen up to the time the comet became lost in the sun's glare after February, while component "E" was seen from September to December. Since "E" was officially discovered in 2000, this could be considered prediscovery observations.

    [Perihelion Date=2001 January 27.72; Period=5.36 years]
    [Images] The comet's next return to perihelion occurred on 2001 January 27. Although it was poorly placed for observation, the comet was again widely observed because it was brighter than expected. In addition, two of the nuclei seen in 1995 were back: Component "C" was recovered on 2000 January 5 and was observed until 2001 November 20, while Component "B" was recovered on 2000 November 19 and was observed until 2001 July 27.

    [Perihelion Date=2006 June 9.53; Period=5.36 years]
    [Images] The next predicted perihelion date is 2006 June 7 and the comet will pass 0.0735 AU from Earth on May 13, being only slightly farther away than during the original discovery apparition of 1930. C. W. Hergenrother (Lunar and Planetary Laboratory) recovered the brightest component, referred to as "C", while using the 1.2-m reflector at Mount Hopkins on 2005 October 22. He gave the magnitude as 19.3 and said the strongly condensed coma was 6 arcsec across. There was also a fan-shaped tail extending 8 arcsec in PA 300°. Component "B" was found at by J. A. Farrell (Jemez Springs, New Mexico, USA) on 2006 January 6, while using a 41-cm reflector. He gave the magnitude as 18.8-19.0, which was then just over three magnitudes fainter than component "C".

    The next component found did not match the prediction for any previously observed component and set the stage for many new discoveries as the comet approached perihelion. This new component was labelled "G". It was independently found by R. A. Tucker (Tucson, Arizona, USA) on February 20 and 22, and E. J. Christensen on Mt. Lemmon Survey images obtained on February 24. The magnitude was given as 17.2. Numerous other components have been found in the weeks that followed and more are expected to be found as the comet nears its closest approach to Earth. Click here for a list of components.

    The major fragments of this comet are "B", "C", "G", and "R", with "C" being the main comet. As the comet headed toward its 2006 close approach to Earth, numerous images were obtained by amateur and professional astronomers which showed additional pieces being shed by these fragments. In particular, fragment "B" displayed a strong coma through April 10, and then the coma narrowed and began extending back into the tail. Shortly after April 20, a new condensation was noted, which steadily moved tailward. A few days later, the coma took on a basically round shape again and a day or two later the new fragment disappeared. As April ended and May began, "B" began to elongate again, but then flared in brightness to become about as bright as the main comet ("C"). Observations of other fragments, including "G" and "R" also revealed multiple changes in the appearance, which were frequently accompanied by the appearance of new fragments. Interestingly, at least through the end of April, there were no confirmed reports of fragments being shed by the main comet and its appearance underwent no unexpected changes.

  • A meteor shower was predicted and observed by Japanese observers during 1930, with an unexpected outburst of 60 or 70 per hour (this is not a corrected zenithal hourly rate, but the raw numbers) occurring on the nights of June 9 and 10. The possibility exists that another outburst could occur in 2006, although the chances for a strong shower actually improve in 2022.
  • Image Library

    Images from the 1995 apparition

    Images from the 2001 apparition

    Images from the 2006 apparition


    List of Components seen since comet split in 1995

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