23P/Brorsen–Metcalf

23P/Brorsen–Metcalf is a periodic comet with an orbital period of 70 years. It fits the classical definition of a Halley-type comet with (20 years < period < 200 years).[1] It was first discovered by Theodor Brorsen at the Altona Observatory on July 20, 1847, and again by Kaspar Schweizer (Moscow) on August 11, 1847. It was predicted that it would reappear between 1919 and 1922.

23P/Brorsen–Metcalf
Comet Brorsen-Metcalf by Edward Emerson Barnard on 6 October 1919
Discovery
Discovered byTheodor Brorsen and Joel Metcalf
Discovery dateJuly 20, 1847
Designations
1847 O1, 1919 Q1, 1989 N1
Orbital characteristics
EpochOctober 1, 1989
Aphelion33.65 AU
Perihelion0.478 AU
Semi-major axis17.07 AU
Eccentricity0.972
Orbital period70.52 yr[1]
69y 8m 28d (perihelion to perihelion)
Max. orbital speed60.2 km/s @ perihelion[2]
Inclination19.33°
Last perihelionSeptember 11, 1989[1]
Next perihelionJune 8, 2059[2][3][4]

On August 21, 1919, the comet was recovered by Joel Hastings Metcalf (Camp Idlewild, Vermont, United States) as 8th magnitude. Additional discoveries were made by Edward Barnard (Yerkes Observatory, Wisconsin, United States) on August 22, Michel Giacobini (Paris, France), Ostrovlev (Theodosia, Crimea) and Selavanov (Saint Petersburg). By the end of September 1919 it was confirmed as being the same as Brorsen's comet.

The comet became visible with naked eye as a small hazy spot of light and on 6 October 1919 it was estimated to have a magnitude of 4.5. The comet had a slender tail with a length of 8,5 degrees. On the photographs of the comet on 22 October 1919 a disconnection event of the tail was visible, that probably started on 20 October.[5]

The comet was recovered by the Palomar Observatory on 4 July 1989, when it had an estimated magnitude of 15, while Alan Hale estimated visually that it had a magnitude of 11.5 on 7 July. The comet brightened rapidly during July and by the end of the month it was reported to have an apparent magnitude of 7-7.5, while developing a short tail. The comet reached its perigee on 6 August, at a distance of 0.62 AU, while its perihelion was on 11 September. Between the two dates the comet had a magnitude between 5 and 6 and was reported to be visible by naked eye. In September the tail grew longer and was reported visually to have a length of about 7 degrees. The comet faded in the second half of September and the diminishing solar elongation hindered further observations.[6] During the 1989 apparition, the comet became the first comet to be definitely detected in submillimeter wavelengths.[7]

References
  1. "JPL Small-Body Database Browser: 23P/Brorsen-Metcalf". Jet Propulsion Laboratory. Retrieved October 17, 2011. last obs. used 1989-09-09
  2. "Horizons Batch for 23P/Brorsen-Metcalf (90000342) on 2059-Jun-08" (Perihelion occurs when rdot flips from negative to positive). JPL Horizons. Archived from the original on 2022-06-27. Retrieved 2022-06-27. (JPL#13 Soln.date: 2002-Mar-01)
  3. Kinoshita, Kazuo (2003-05-29). "23P/Brorsen-Metcalf past, present and future orbital elements". Comet Orbit. Retrieved 2023-07-29.
  4. Seiichi Yoshida (2005-11-09). "23P/Brorsen-Metcalf". Seiichi Yoshida's Comet Catalog. Retrieved February 19, 2012.
  5. Barnard, E. E. (1 March 1920). "On Comet 1919b and on the Rejection of a Comet's Tail". The Astrophysical Journal. 51: 102. Bibcode:1920ApJ....51..102B. doi:10.1086/142527. ISSN 0004-637X.
  6. Kronk, Gary W. (2017). Cometography. Volume 6: 1983–1993. West Nyack: Cambridge University Press. pp. 432–435. ISBN 9781139033947.
  7. Jewitt, David; Luu, Jane (December 1990). "The submillimeter radio continuum of Comet P/Brorsen-Metcalf". The Astrophysical Journal. 365: 738. doi:10.1086/169527.
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