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 by	Theodor Brorsen and Joel Metcalf
Discovery date	July 20, 1847
Designations
Alternative designations	1847 O1, 1919 Q1, 1989 N1
Orbital characteristics
Epoch	October 1, 1989
Aphelion	33.65 AU
Perihelion	0.478 AU
Semi-major axis	17.07 AU
Eccentricity	0.972
Orbital period	70.52 a[1]
Inclination	19.33°
Last perihelion	September 11, 1989[1]
Next perihelion	June 8, 2059[2][3]

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.[4]