 The comet on 30 March 1894 byMax Wolf | |
| Discovery[1] | |
|---|---|
| Discovered by | William F. Denning |
| Discovery site | Bristol, England |
| Discovery date | March 26, 1894 |
| Designations | |
| D/1894 F1 P/2007 HE4 | |
| 1894 I, 1894a | |
| Orbital characteristics[2] | |
| Epoch | 18 August 2002 (JD 2452504.5) |
| Observation arc | 113.14 years |
| Number of observations | 302 |
| Aphelion | 7.312 AU |
| Perihelion | 1.575 AU |
| Semi-major axis | 4.443 AU |
| Eccentricity | 0.6456 |
| Orbital period | 9.37 years |
| Inclination | 4.007° |
| 22.579° | |
| Argument of periapsis | 107.96° |
| Mean anomaly | 180.38° |
| Last perihelion | 2 September 2016 |
| Next perihelion | 4 December 2025 |
| TJupiter | 2.579 |
| EarthMOID | 0.596 AU |
| JupiterMOID | 0.065 AU |
| Comet total magnitude (M1) | 7.6 |
489P/Denning is aJupiter-family comet with an orbital period of 9.4 years. It was discovered byWilliam Frederick Denning on 26 March 1894 but was subsequentlylost until 2024, when asteroid2007 HE4 was identified as the same object.[3]
William Frederick Denning was searching for comets fromBristol, England, when on 26 March 1894 he found a faint object inLeo Minor.[a] The next few days the magnitude of the comet was reported to be about 11. The comet also featured a tail about 5 arcminutes long. The comet upon discovery had passed both theperihelion and closest approach to Earth and was becoming fainter. In April the comet was observed as very faint and elongated. Few observations were made in May. The comet was last detected on 5 June 1894.[4] It is possible the comet experienced an outburst in 1894.[3]
The first orbit was calculated byLipót Schulhof with positions from 27 to 31 March and indicated a parabolic orbit with perihelion on 13 February 1894. However, by mid April he suspected that the comet deviated from the orbit. The first elliptical orbit he calculated, with positions from 27 March to 25 April, had a perihelion date of 9 February and an orbital period of 6.74 years. Other orbits calculated were 7.94 years byLewis Boss, 6.79 years by Schulhof, 6.76 years byJohn Russell Hind, and 7.70 years by Hind.[4]
The comet wasn't recovered and becamelost. In 2024 it was noted that Mars-crossing asteroid2007 HE4, which was discovered byLINEAR on 17 April 2007 with an apparent magnitude of 18.7–19.5, had a comet-like orbit[3] and was ranked by a machine learning model as likely active due to only being observed on one opposition.[5]Maik Meyer found that the asteroid's orbit was a good match with the proposed orbit of comet Denning.[3] Images of the object by the Great Shefford Observatory from 18 and 19 April were re-examined and it appeared slightly elongated, with an aspect ratio of 3:2 when compared with nearby stars, and extending eastwards.[6] Images obtained by the 1.82 m (6.0 ft) telescope of theDominion Astrophysical Observatory on 19 April 2007 when stacked showed a coma with a diameter of 5".3 and a faint, spike-like tail extending for 8 arcseconds. The apparitions from 1972 to 1997 weren't favorable. The 1963–4 apparition was favorable, however no plates were found.[3]
During the 2025 apparition the comet is predicted to reach 18th magnitude.[3]
As a Jupiter-family comet, 489P/Denning approaches close to planetJupiter. A close approach, at a distance of 0.071 AU (10.6 million km) took place in July 1830. During the 1894 apparition the comet had a perihelion distance of 1.15 AU and an orbital period of 7.42 years. An approach to Jupiter on 18 June 1925 at a distance of 0.24 AU raised the orbital period to 8.00 years and perihelion to 1.29 AU and a further approach on 8 November 1986 at a distance of 0.19 AU raised them to 9.31 years and 1.56 AU respectively.[3]
During the 1894 apparition the comet passed 0.27 AU (40 million km) from Earth on 12 February.[7] Other close encounters took place on 25 December 1908, at a distance of 0.62 AU, and on 29 January 1964 at a distance 0.47 AU.[3]
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