 Comet Brorsen–Metcalf photographed byEdward E. Barnard on 6 October 1919 | |
| Discovery | |
|---|---|
| Discovered by | Theodor Brorsen Joel Metcalf |
| Discovery site | Altona Observatory |
| Discovery date | 20 July 1847 |
| Designations | |
| |
| |
| Orbital characteristics[4][5] | |
| Epoch | 1 October 1989 (JD 2447800.5) |
| Observation arc | 142.11 years |
| Number of observations | 250 |
| Aphelion | 33.65 AU |
| Perihelion | 0.478 AU |
| Semi-major axis | 17.07 AU |
| Eccentricity | 0.972 |
| Orbital period | 70.546 years |
| Max.orbital speed | 60.2 km/s[1] |
| Inclination | 19.336° |
| 311.59° | |
| Argument of periapsis | 129.61° |
| Mean anomaly | 0.266° |
| Last perihelion | 11 September 1989 |
| Next perihelion | 8 June 2059[1][2][3] |
| TJupiter | 1.109 |
| EarthMOID | 0.194 AU |
| Physical characteristics[6] | |
Mean radius | <5.0 km (3.1 mi) |
| Comet total magnitude (M1) | 7.8 |
| Comet nuclear magnitude (M2) | 14.0 |
23P/Brorsen–Metcalf is aperiodic comet with an orbital period of 70 years. It fits the classical definition of aHalley-type comet.[4]
It was first discovered byTheodor Brorsen at theAltona Observatory on 20 July 1847, and again byKaspar Schweizer (Moscow) on 11 August 1847.[7] It was predicted that it would reappear between 1919 and 1922
On 21 August 1919, the comet was recovered byJoel Hastings Metcalf (Camp Idlewild,Vermont, United States) as 8thmagnitude.[8] Additional discoveries were made byEdward Barnard (Yerkes Observatory,Wisconsin, United States) on 22 August,Michel Giacobini (Paris, France),Ostrovlev (Theodosia,Crimea) andSelavanov (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.[9]
The comet was recovered by thePalomar Observatory on 4 July 1989, when it had an estimated magnitude of 15, whileAlan 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 (93 million km), 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 diminishingsolar elongation hindered further observations.[10] During the 1989 apparition, the comet became the first comet to be definitely detected insubmillimeter wavelengths.[11] Spectroscopic and infrared photometric observations conducted between 28 August and 6 September 1989 from theNASA Infrared Telescope Facility of theMauna Kea Observatory in Hawaii obtained an upper limit of the radius of itsnucleus at no greater than 5.0 km (3.1 mi).[6]
| Numbered comets | ||
|---|---|---|
| Previous 22P/Kopff | 23P/Brorsen–Metcalf | Next 24P/Schaumasse |
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