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D/1918 W1 (Schorr)

Discovery

In an attempt to photograph the minor planet 232 Russia, R. R. E. Schorr (Hamburg Observatory, Bergedorf, Germany) discovered this comet on a plate exposed with a 100-cm reflector on 1918 November 23.82. The comet was confirmed on another photographic plate exposed with the same telescope on November 24.81. It was described as magnitude 14.0, with a coma 30 arc seconds across on both dates.

Historical Highlights

  • The comet had passed perihelion nearly two months earlier and had passed closest to Earth a week before discovery. M. F. J. C. Wolf (Königstuhl Observatory, Heidelberg, Germany) estimated the magnitude as 14.0 on November 30. On December 1, E. E. Barnard (Yerkes Observatory, Wisconsin, USA) estimated the magnitude as 15 and said the coma was 1 arc minute across. Barnard also gave the magnitude as 15-15.5 on the 4th and 16 on the 6th. On the former date, he noted the coma was 1 arc minute across and exhibited very little condensation. On the 7th, H. C. Wilson (Goodsell Observatory, Carleton College, Minnesota, USA) said the comet was initially not visible in the 41-cm refractor, but finally glimpsed it "after prolonged looking and averted vision." He said it was 30 arc seconds across, but he saw no nucleus. For the 8th, Barnard wrote, "Excessively faint in bad sky." On December 21, 24, and 26, Schorr estimated the magnitude as 15.0. The comet was last detected on December 31.97, when Schorr gave the estimate as 15.0.
  • The first orbit was calculated by S. E. Strömgren using positions up to November 30. It was a parabolic orbit with a perihelion date of 1918 August 8.41. A couple of days later, H. M. Jeffers calculated the first elliptical orbit using positions up to December 1. The result was a perihelion date of October 8.79 and a period of 6.71 years. During the next couple of weeks, Jeffers determined the perihelion date as October 16.94 and the period as 5.86 years, while J. Braae and J. Fischer-Petersen determined the perihelion date as September 28.08 and the period as 6.73 years.
  • Orbits using positions spanning the entire period of visibility have been computed by Jeffers (1919), J. Larink (1925, 1926), C. de Vegt, L. Kohoutek, and B. G. Marsden (1982), S. Nakano (2001), and K. Kinoshita (2003). Jeffers determined the perihelion date as September 30.67 and the period as 6.68 years. Larink determined the perihelion date as September 29.10 and the period as 6.71 years. De Vegt, Kohoutek, and Marsden remeasured the photographic plates obtained in 1918. They determined the perihelion date as September 30.25 and the period as 6.67 years. Using the remeasured positions, Nakano gave the perihelion date as September 30.14 and the period as 6.67 years, while Kinoshita gave the perihelion date as September 30.24 and the period as 6.67 years.
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