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Past, Present, and Future Orbits by Kazuo Kinoshita


     While sweeping for comets with either Zeiss binoculars or a small telescope, Walter Frederick Gale (Sydney, Australia) found a "very small faint nebulosity preceding Theta Piscis Australis," on 1927 June 7.60. He estimated the magnitude as about 8.0 and gave the coma diameter of 3 arc minutes. After examining the object with a telescope, Gale was convinced he had found a comet and immediately announced his discovery by telegram.

Historical Highlights

  • Apparition of 1927: The comet was at its maximum brightness when discovered and it faded very slowly during the remainder of its apparition. It was last detected on September 2 at Johannesburg. The majority of the observations were made at observatories in Africa, namely, from the Cape of Good Hope and Johannesburg in South Africa, and Algiers in Algeria. The comet was never seen in the larger United States or European observatories. George van Biesbroeck (Yerkes Observatory, Wisconsin, USA) failed to visually detect the comet on September 17, and a photograph of the comet's expected position on October 17 failed to reveal it despite showing stars to magnitude 16.
  • The first orbits were computed during July 1927. Even the earliest ones indicated the comet passed perihelion on June 14 at a distance of 1.3 AU. Harry Edwin Wood (Johannesburg, South Africa) computed the first elliptical orbit using observations from June 10 to 24. This indicated the perihelion date was June 14.6, the perihelion distance was 1.22 AU, and the orbital period was 11.85 years. Shortly thereafter, R. T. A. Innes computed a similar elliptical orbit using the same span of observations, but with an orbital period of 16.28 years. Before the end of 1927, astronomers had narrowed the orbital period down to 11.11 years. A definite orbit computed in 1930 by Maud Worcester Makemson indicated a period of 11.03 years.
  • Apparition of 1938: The comet was next expected to arrive at perihelion during 1938. Gale announced in early April of that year that he had failed to detect the comet during 20 mornings of searches. On April 26 Leland E. Cunningham published a revised prediction indicating the comet would pass perihelion on May 16.90. He added that he felt it was 99 percent likely that the comet would pass perihelion within 30 days of his prediction. Interestingly, Cunningham made the actual recovery of this comet on May 1.24 at Oak Ridge observatory. He described it as magnitude 10, with a central condensation 30" across and a faint coma 100 arc seconds in diameter. His measured position indicated his prediction was 32.6 days too early, which was the best prediction for this apparition. The comet was observed until July 29.89, when Ernest Leonard Johnson (Union Observatory, Johannesburg, South Africa) photographed it. Although van Biesbroeck indicated the comet steadily faded from magnitude 11 to 12 during May and June, several observers reported the comet at magnitude 9 and 10 during the latter half of June. In addition, even though the comet was moving away from both the sun and Earth after early June, Johnson estimated the magnitude as 8.5 on July 20--just nine days before his final observation! Some astronomers have suggested the comet underwent a minor outburst at that time. Johnson attempted to photograph the comet again on August 16 and 18, but was unsuccessful.
  • Predictions following the 1938 apparition: Predictions were made for the 1949 apparition and although a half dozen observatories searched for the comet both visually and photographically, the comet was not found. The resulting conclusions were that either the comet was far off its predicted course or it was much fainter than expected. Johnson reexamined photos taken in 1927 and 1938 and noted the comet was much more diffuse in the latter year than in the former, with a condensation only noted on one occasion in 1938. Predictions were made for the apparitions of 1960, 1970, 1981, and 1992, but the placement of the comet's perihelion was not considered favorable at any of these and few, if any, searches were made. An example of the poor placement can be taken from the 1992 predictions. By the time the comet had become brighter than magnitude 20 it was already less than 45 degrees from the sun. At its brightest predicted magnitude of 14.4 it was less than 6 degrees from the sun. B. G. Marsden has conjectured that although the orbit may have been well established after the 1927 and 1938 returns, nongravitational forces could push the actual perihelion passage several weeks either side of the more recent predictions, so that long-exposure photographic attempts to detect the comet when faint and at larger solar elongations could miss the comet by several degrees.
  • Close approaches to planets: Although there is uncertainty as to the comet's location after so many years of being lost, the following information is based on an orbit that fits the 1927 and 1938 positions best and will give some indication of the comet's movement. (From the orbital work of Kazuo Kinoshita)
    • 0.11 AU from Jupiter on 1917 August 5
      • increased perihelion distance from 1.18 AU to 1.21 AU
      • decreased orbital period from 11.43 to 11.28 years
    • 0.35 AU from Earth on 1927 June 7
      • contributed to comet's discovery
    • 1.40 AU from Jupiter on 1929 May 25
      • decreased perihelion distance from 1.21 AU to 1.18 AU
      • decreased orbital period from 11.28 to 10.99 years
    • 0.25 AU from Earth on 1938 June 7
    • 1.53 AU from Saturn on about 1945 April 19
    • 0.95 AU from Jupiter on about 1991 April 23