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25D/Neujmin 2

Past, Present, and Future Orbits by Kazuo Kinoshita

Hamburg image of 25D obtained on 1916 April 2/3
Copyright © 2010-2015 Hamburger Sternwarte

This image of comet Neujmin 2 was obtained on 1916 April 2/3 with the 1-m reflector at Hamburg Observatory. A 9x12 photographic plate was exposed for 10 minutes, while the telescope was guided on the comet. (The image was cropped and inverted.)


     During the course of a routine photographic minor planet survey, Grigory N. Neujmin (Simeis) discovered this comet on 1916 February 24.78. Neujmin found the object about 1.5° from the north border of the plate and noted it was about 2 arc minutes long and inclined a little from the circle of declination. The presence of weak nebulosity north and south of the trail confirmed that the object was a comet. He estimated the magnitude as 11. George van Biesbroeck (Yerkes Observatory, Wisconsin, USA) confirmed the comet on March 1.11, and Dyson (Greenwich Observatory, England) saw it on March 1.85. The latter astronomer estimated the magnitude as 11.0.

Historical Highlights

  • The comet was very near perihelion when discovered. Several observers gave the total magnitude as 11 during the first days of March, but the comet faded thereafter. It was last detected on June 5, when Neujmin detected a faint trace on a photograph.
  • In the February 1921 issue of The Observatory, A. C. D. Crommelin pointed out that this comet was due back at perihelion in September, but would be "so badly placed that its detection is improbable." No observations were reported.
  • B. F. Bawtree had a prediction published in the British Astronomical Association Handbook for 1927 which gave the perihelion date as 1927 January 2.37. He had applied perturbations by Jupiter. Bawtree included a second prediction based on an assumption than an object reported in November of 1920 (nearly a year before the expected perihelion passage) was this comet. The resulting perihelion date was 1927 January 24.37.
  • The comet has not been seen since the 1927 apparition. Crommelin corrected Neujmin's orbit for the 1927 return and predicted the next perihelion date as 1932 June 19.63. The said the comet was poorly placed and was not expected to be found. An unsuccessful search did take place at Bergedorf. For the 1937 apparition, Neujmin predicted a perihelion date of November 21.25 and F. R. Cripps predicted a date of November 24.58. On November 11, George van Biesbroeck (Yerkes Observatory, Wisconsin, USA) photographed the region where the comet was expected to lay, but nothing unusual was found, despite stars to magnitude 15 being visible. Van Biesbroeck added, however, that Neujmin predicted the comet's brightness to be 15-16 at that time. Further predictions were published by Cripps for the 1943 and 1948 returns, but no searches appear to have taken place.
  • Close approaches to planets: With the comet having been lost for so long an extensive list of close approaches can not be considered very reliable. Kazuo Kinoshita (1998) calculated a set of orbits based on the addition of nongravitational effects, which proved to fit the available positions from 1916 and 1927 better than calculations without these effects. These orbits indicate the comet made three close approaches to Earth and one close approach to Jupiter during the first half of the 20th century. Orbits purely gravitational, as well as nongravitational effects indicate that from about 1965 to 2019, the perihelion distance is less than it was when seen in 1916 and 1927. (From the orbital work of Kazuo Kinoshita)
  • 0.38 AU from Earth on 1916 February 25 (contributed to comet's discovery)
  • 0.79 AU from Earth on 1927 April 12
  • 0.80 AU from Earth on 1943 January 22
  • 0.93 AU from Jupiter on 1950 August 9
    • increased perihelion distance from 1.35 AU to 1.44 AU
    • increased orbital period from 5.43 to 5.61 years