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23P/Brorsen-Metcalf

Past, Present, and Future Orbits by Kazuo Kinoshita

Bill and Sally Fletcher photo of 23P obtained in 1989
Copyright © 1989 by Bill and Sally Fletcher

This photograph was taken during the 1989 apparition of this comet, using a 16-inch f/4.5 Newtonian telescope and Tech Pan film. Other comet images, as well as numerous deep sky objects can be found on their website.

Discovery

     The comet was discovered on 1847 July 20, when Theodor Johann Christian Ambders Brorsen (Altona, Germany) found it in Aries while sweeping for comets in the morning sky. He described it as a weak nebulosity, without a noticeable condensation, and noted its movement toward the northeast. The comet was independently discovered by K. G. Schweizer (Moscow) on August 11, when it was described as round, without a tail. Although it was obvious the comet moved in an elliptical orbit, estimates of the orbital period ranged from 71 to 99 years, with 71 to 75 years seeming most likely. Predictions were made indicating the comet would return sometime between 1919 and 1922.
     During a routine search for comets, the Reverend Joel H. Metcalf (Camp Idlewild, South Hero, Vermont, USA) discovered this comet shortly before sunrise on 1919 August 21, just west of the Great Square of Pegasus. It was described as 8th magnitude. The comet was confirmed by Edward Emerson Barnard (Yerkes Observatory, Wisconsin, USA) on August 22, and was described as "very large and diffuse," with "an ill-defined, faint condensation" of magnitude 15. Barnard added that the coma was "slightly more condensed in (the) south preceding side." Independent discoveries were made by Giacobini (Paris, France) on August 22, Ostrovlev (Theodosia, Crimea) on August 28, and Selavanov (St. Petersburg) on September 2. During the final days of August and first days of September astronomers suggested and then confirmed a link to Brorsen's comet.

Historical Highlights

  • Apparition of 1847: During 1847 the comet passed closest to Earth on August 6 (0.65 AU) and passed perihelion on September 10 (0.49 AU). Although passed Earth, the comet continued to brighten as it approached the sun. Although magnitude estimates were not available, some reasonable guesses based on the comet's discovery and final observation would indicate the maximum brightness might have reached 8. The maximum reported tail length was one-fourth degree. The comet was not seen after September 13.
  • Apparition of 1919: The comet became a naked-eye object in early September and attained a maximum magnitude of about 4.5 in early October. Around the time of the closest approach to Earth the comet's coma was reported as about 25 arc minutes across, or nearly equal to the apparent width of the moon (30 arc minutes). No tail was detected until early October and grew to a maximum length of 8.5 degrees by mid-October. Thereafter the comet faded and the tail length decreased. The comet was lost in morning twilight after November 18.
  • Apparition of 1989: During 1989 the comet passed closest to Earth on August 7 and passed perihelion on September 11 (0.48 AU). Between these two dates the comet attained a maximum magnitude near 5.
  • Close approaches to planets: This comet made two close approaches to Earth and one close approach to Saturn during the 20th century. (From the orbital work of Gary W. Kronk)
    • 1.68 AU from Saturn on 1901 August 4
    • 0.20 AU from Earth on 1919 September 6
    • 0.62 AU from Earth on 1989 August 7

    Additional Images

    G. Rhemann image of 23P on 1989 September 1
    Copyright © 1989 by Gerald Rhemann (Austria)

    This photograph was taken by Rhemann on 1989 September 1, using a 180/2.8 Zeiss Sonnar and hypered Technical Pan 2415. This is a composite of two 7-minute exposures.

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