84P/Giclas
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- D/1931 R1,[2] P/1978 R2
- P/1985 M1
 Comet Giclas photographed from the Zwicky Transient Facility on 14 August 2020 | |
| Discovery[1] | |
|---|---|
| Discovered by | Henry L. Giclas |
| Discovery site | Lowell Observatory, USA |
| Discovery date | 8 September 1978 |
| Designations | |
| |
| |
| Orbital characteristics[3][4] | |
| Epoch | 21 November 2025 (JD 2461000.5) |
| Observation arc | 89.43 years |
| Earliest precovery date | 12 September 1931[5] |
| Number of observations | 1,792 |
| Aphelion | 5.381 AU |
| Perihelion | 1.719 AU |
| Semi-major axis | 3.550 AU |
| Eccentricity | 0.51562 |
| Orbital period | 6.689 years |
| Inclination | 7.553° |
| 108.08° | |
| Argument of periapsis | 281.74° |
| Mean anomaly | 293.89° |
| Last perihelion | 3 June 2020 |
| Next perihelion | 12 February 2027[6] |
| TJupiter | 2.872 |
| Earth MOID | 0.862 AU |
| Jupiter MOID | 0.555 AU |
| Physical characteristics[3] | |
Mean radius | 0.90 ± 0.05 km (0.559 ± 0.031 mi)[7] |
| 0.04 (assumed) | |
| (V–R) = 0.32±0.03[7] | |
| Comet total magnitude (M1) | 14.2 |
84P/Giclas is a Jupiter-family comet with a 6.69-year orbit around the Sun. It is the only comet discovered by American astronomer, Henry L. Giclas.
1931 apparition
It was announced in 1995 that Clyde W. Tombaugh had observed a previously unknown comet for three nights in September 1931.[5] Designated as D/1931 R1,[2] it was later confirmed to be an earlier apparition of 84P/Giclas upon reconstructing its orbit using non-gravitational accelerations in a 1996 study by Grzegorz Sitarski.[8]
1979 apparition
The comet was discovered by Henry L. Giclas from the Lowell Observatory on 8 September 1978.[1] At the time it was a diffuse 15th-magnitude object within the constellation Cetus.[a] He confirmed his discovery about two days later,[10] where Brian G. Marsden soon determined that it follows a 6.74-year periodic orbit around the Sun.[11] Throughout its 1978–1979 apparition, it remained mostly a photographic object.[9]
Follow-up observations
During the 2020 apparition, it was not more than 60 degrees from the Sun until September 2020. On 11 June 2033, the comet will pass 0.0387 AU (5.79 million km; 3.60 million mi) from the asteroid 4 Vesta.[3]
Physical characteristics
Based on observations by the Hubble Space Telescope in 1999–2000, the nucleus of the comet has a radius of 0.90±0.05 km, assuming a geometric albedo of 0.04.[7]
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