Comet Encke
 |
|
| Discovery | |
|---|---|
| Discovered by |
Pierre Méchain; Johann Franz Encke (recognition of periodicity) |
| Discovery date | 17 January 1786 |
| Alternative designations |
1786 I; 1795; 1805; 1819 I; 1822 II; 1825 III; 1829; 1832 I; 1835 II; 1838; 1842 I; 1845 IV |
| Orbital characteristics A | |
| Epoch | September 22, 2006 (JD 2454000.5) |
| Aphelion | 4.11 AU |
| Perihelion | 0.3302 AU |
| Semi-major axis | 2.2178 AU |
| Eccentricity | 0.8471 |
| Orbital period | 3.30 a |
| Inclination | 11.76° |
| TJupiter | 3.026 |
| Dimensions | 4.8km |
| Last perihelion | 21 November 2013 |
| Next perihelion | 10 March 2017 |
Comet Encke or Encke's Comet (official designation: 2P/Encke) is a periodic comet that completes an orbit of the Sun once every 3.3 years. (This is the shortest period of a reasonably bright comet; the faint main-belt comet 311P/PANSTARRS has a period of 3.2 years.) Encke was first recorded by Pierre Méchain in 1786, but it was not recognized as a periodic comet until 1819 when its orbit was computed by Johann Franz Encke; like Halley's Comet, it is unusual in being named after the calculator of its orbit rather than its discoverer. Like most comets, it has a very low albedo, reflecting only 4.6% of the light it receives. The diameter of the nucleus of Encke's Comet is 4.8 km.
As its official designation implies, Encke's Comet was the first periodic comet discovered after Halley's Comet (designated 1P/Halley). It was independently observed by several astronomers, the second being Caroline Herschel in 1795 and the third Jean-Louis Pons in 1818. Its orbit was calculated by Johann Franz Encke, who through laborious calculations was able to link observations of comets in 1786 (designated 2P/1786 B1), 1795 (2P/1795 V1), 1805 (2P/1805 U1) and 1818 (2P/1818 W1) to the same object. In 1819 he published his conclusions in the journal Correspondance astronomique, and predicted correctly its return in 1822 (2P/1822 L1). It was recovered by Carl Ludwig Christian Rümker at Parramatta Observatory on 2 June 1822.
Comets are in unstable orbits that evolve over time due to perturbations and outgassing. Given Encke's low orbital inclination near the ecliptic and brief orbital period of 3 years, the orbit of Encke is frequently perturbed by the inner planets.
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