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5D/Brorsen

Past, Present, and Future Orbits by Kazuo Kinoshita

Discovery

     Theodor Brorsen (Holstein, Germany) discovered this telescopic comet on 1846 February 26, near Eta Piscium. He was then conducting a routine search for comets.

Historical Highlights

  • This comet remained visible for nearly two months during its discovery apparition. It had passed perihelion on February 25, just one day prior to its discovery, and continued to approach Earth thereafter. It passed closest to our planet on March 27 (0.52 AU). The comet's coma diameter increased as a result of this close approach, with Johann Friedrich Julius Schmidt (Bonn) estimating it as 3 to 4 arcmin across on March 9, and 8 to 10 arcmin across on March 22. The comet was last seen on April 22, when it was situated less than 20 degrees from the north celestial pole. The comet was first recognized as a short-period comet while still being observed in March. Although Johann Franz Encke then gave the orbital period as 3.44 years because of barely one week of observations, the period had been pinpointed as about 5.5 years before the end of the month.
  • Later calculations revealed the comet was pulled into its discovery orbit as a result of a close approach to Jupiter (0.0668 AU) during 1842 May.
  • The comet was next expected to arrive at perihelion during 1851 September, but searches proved fruitless. An analysis of this apparition revealed the comet only came as close as 1.31 AU from Earth during late August, making this a very unfavorable apparition. The comet's 5.5-year period would cause apparitions to alternate between very favorable and very poor.
  • With only one observed apparition, the predictions for the 1857 return were considered somewhat uncertain, especially since the comet had passed 0.84 AU from Jupiter during 1854. Interestingly, Karl Christian Bruhns (Berlin, Germany) discovered a comet on 1857 March 18.80. He described it as round and 2 arcmin across. It exhibited a condensed nucleus, but no tail. After a few days of observations the first orbits were computed. Pape noted a strong similarity to the expected comet Brorsen and this was confirmed during April. The predictions had been three months off. As it turned out, the comet was then about 10 days from passing perihelion and would pass 0.73 AU from Earth during early May. These circumstances allowed the comet to change little in brightness for about two months following recovery. Observations continued until June 23, so that the comet's orbit was now very well known.
  • The comet was again badly placed during its next apparition in 1862, and although it passed 1.3 AU from Jupiter during 1866, it was recovered very close to the predicted position during 1868. By this time the comet's orbital period had dropped slightly below 5.5 years and this enabled the comet to be recovered during 1873. The 1879 apparition was again very favorable and the comet was observed for 4 months--the longest observed apparition to date.
  • This comet has not been seen since 1879. Another unfavorable apparition in 1884 was followed by a very favorable apparition in 1890, but searches revealed no comet. Another unfavorable return came in 1895 and that was followed by another very favorable return in 1901. Intensive searches at the latter apparition revealed nothing. No serious searches were conducted for the next few decades. The comet should have passed 0.37 AU from Jupiter during 1913 July. B. G. Marsden considered these failed searches as telltale signs that the comet had "faded out of existence" when he set out to redetermine the orbit of this comet in 1963. Nevertheless, he integrated the orbit up to the very favorable 1973 apparition. Japanese observers conducted several searches during 1973, but failed to locate the comet.
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