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109P/Swift-Tuttle

Past, Present, and Future Orbits by Kazuo Kinoshita

H. Mikuz image of 109P exposed on 1992 December 15
Copyright © 1992 by Herman Mikuz (Crni Vrh Observatory, Slovenia)

This image was obtained on 1992 December 15, with 3.5/250mm lens, CCD, and narrow-band H2O+ filter, centered at 620nm (FWHM=10nm). The field of view is 2.9x1.9 degrees. (The webmaster has inverted the image to better represent the appearance of the comet.)

Discovery

Lewis Swift (Marathon, New York, USA) discovered this comet in Camelopardalis on 1862 July 16, while examining the northern sky with his 11.4-cm Fitz refractor. He described the comet as a somewhat bright telescopic object, but did not report it since he thought he was observing the comet Schmidt had found on July 2. Without knowledge of Swift's observation, Horace Parnell Tuttle (Harvard College Observatory, Cambridge, Massachusetts, USA) independently discovered this comet on July 19.19 and noted it was heading northward. He then made an official announcement. When Swift heard of Tuttle's find, he immediately realized the comet seen on July 16 was not Schmidt's and made his announcement to get credit for his first comet discovery.

Historical Highlights

  • There were several independent discoveries. Thomas Simons (Dudley Observatory, Albany, New York, USA) independently discovered the comet on July 19.30. He remarked, "When first seen it appeared as a nebula considerably condensed at the centre, the light being intense enough to be easily observed when the wires of the micrometer were illuminated." Antonio Pacinotti and Carlo Toussaint (Florence, Italy) found the comet on July 22. Schjellerup (Copenhagen) found this comet in Camelopardalis on the night of July 26/27. He described it as a bright nebulosity with a very slow movement. On July 27.98, Schjellerup and d'Arrest confirmed the discovery with a large refractor. Schjellerup remarked, "The comet is rather bright, the nucleus equalled a star of 7th magnitude." He added that at a magnification of 226x they saw a distinct extension in the direction of the sun, while the surrounding nebulosity was 3 arc minutes across. On September 1, John Tebbutt (Windsor, New South Wales) independently discovered this comet, not yet having received a notification of its prior discovery. With a 3.25-inch telescope, he noted the comet's nucleus was badly defined and did not admit accurate determinations of position.
  • J. F. Julius Schmidt (Athens, Greece) made numerous observations of the comet from 1862 August to September. He examined his magnitude estimates of the comet's nucleus and determined that, on the average, maximum light occurred every 2.691±0.269 days, while minimum light occurred every 2.711±0.284 days.
  • The earliest orbits were computed at the end of July and in early August. These were parabolic orbits indicating a perihelion date of 1862 August 22 to 24. During the next few years several astronomers computed elliptical orbits indicating an orbital period between 120 and 125 years, with the first attempt at a definitive orbit coming in 1889 when F. Hayn determined the orbital period as 119.64 years. During 1971, B. G. Marsden and Zdenek Sekanina took 212 positions obtained during the period of 1862 July 22 to October 22, applied perturbations by all nine planets, and determined the orbital period as 119.98 years. A couple of years later, Marsden looked at the possibility of trying to link Swift-Tuttle to an earlier comet. He found two in the 18th century that looked promising--1737 (Kegler) and 1750 (Wargentin). The 1750 comet appeared at just about the right time expected for Swift-Tuttle if that comet's motion was integrated back from 1862. The problem, however, was that it was moving too fast. The 1737 comet actually exhibited a motion consistent for what would have been expected for Swift-Tuttle if the perihelion date had fallen on June 15 of that year; however, as Marsden pointed out, the main point this identity "is that the comet's osculating period would have to have been some 10 yr longer than is indicated by the observations in 1862." Marsden made two predictions for a forthcoming return. First, using the definitive orbit of Sekanina and himself, he suggested a perihelion date of 1981 September 16.93. Second, he suggested that if the link to the comet of 1737 was valid, the comet would likely return to perihelion on 1992 November 25.85.
  • Minor searches for the comet began in 1980, which was within the error range given by calculations, and more rigorous searches were conducted in 1981 and 1982, but nothing was found.
  • Tsuruhiko Kiuchi (Japan) discovered a comet on 1992 September 26.76 and reported it to the National Astronomical Observatory (Tokyo). He said it was magnitude 11.5. H. Kosai of that observatory subsequently reported it to the (Central Bureau for Astronomical Telegrams) and suggested it might be comet Swift-Tuttle. Several observers were able to confirm the comet within the next 24 hours and the indicated direction and rate of motion was consistent with what would be expected for Swift-Tuttle. Brian G. Marsden (Central Bureau) was not able to do a precise linkage between the 1862 and 1992 positions, but he did provide an orbit that adequately represented all available positions. It indicated a perihelion date of 1992 December 12.29, a perihelion distance of 0.959 AU, and an orbital period of 135.29 years.
  • Observations made within the first days following the recovery revealed the comet's actual magnitude was near 9 and that the coma diameter was about 4 arc minutes.The comet steadily brightened during the following weeks. It surpassed magnitude 8.5 shortly after October began and had climbed to 6.0 by the beginning of November. A faint tail over a degree long was already visible on photographs after mid-October and this continued to brighten during the following weeks. By mid-November it was possible to see over 2 degrees of tail with binoculars. Along other lines of observation, astronomers reported that observations during the first half of November were revealing the production rates of various gases, of which OH, Methanol, CS, and water were among the first identified.
  • The comet surpassed magnitude 5.0 right at mid-November and continued brightening. The ion tail was 6.7 degrees long on November 23 when Herman Mikuz (Slovenia) imaged it with 10-minute exposure CCD frames. Most interesting was a report by L. Jorda and J. Lecacheux (Paris-Meudon) and F. Colas (Observatoire de Paris) that observations of a nuclear jet with the 1.05-m telescope and CCD camera at Pic du Midi over the period of November 20-26 indicated a probable nuclear rotation period of 2.9 days. Compare this to the periodicity earlier noted by Schmidt in the brightness of the nucleus back in 1862. As November came to a close brightness estimates were still at 5.0 and the comet showed no sign of fading until just before mid-December.
  • G. Rhemann image of 109p exposed on 1992 November 24
    Copyright © 1992 by Gerald Rhemann

    This image was obtained on 1992 November 24.74 UT with the 171/200/257mm Schmidt camera. Exposure time was 10 minutes and the photographic emulsion was Kodak Ektachrome 100. The comet's total magnitude was then about 5.0. (The image has been cropped by the webmaster to save space.)

  • By early December of 1992 it was becoming obvious that independent orbital calculations by Marsden and Donald K. Yeomans which attempted to fit the 1862 and 1992 observations were becoming increasing further off the mark in predicting the motion of this comet. Marsden attempted a nongravitational solution and managed the best fit of the available positions, but noted large discrepancies in the positions of 1862 October. Interestingly, this new orbit allowed two prediscovery images to be located. The first was found by R. Haver (Cima Ekar) on a plate exposed with a 0.4-m f/2.5 Schmidt on 1992 January 3.08. The comet was described as stellar with a magnitude of 17.5. The second was found by L. Kohoutek (Calar Alto) on a plate exposed on January 7.09 with a 0.8-m Schmidt. He estimated the magnitude as 18. Around this time, Gary Kronk (Troy, Illinois, USA) announced the liklihood that comets reported by the Chinese in -68 and +188 were good candidates for Swift-Tuttle. Independent computations by Marsden and G. Waddington (Oxford University) confirmed the links and noted a purely gravitational solution worked better to fit the apparitions. In addition, it was realized that no favorable apparitions would have occurred following 188 until 1737.
  • The comet was last seen on 1995 March 29.48, by observers at Siding Spring Observatory (Australia).
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