A comet appearing very bright in the night sky was first discovered by Pierre Mechain (France) on 17th January, 1786 in the Aquarius constellation. The comet was confirmed by 19th January, 1786 but no observations were made after 19thJanuary. However, it was again discovered by Caroline Herschel (England), who had confirmed it to be a comet by her brother William Herschel on 7th November, 1795. The third discovery of the comet was made by Jean Louise Pons (France) on 20th October, 1805. Also, independent discoveries were made by Johan Sigismund Huth (Germany) on 21st and by Alexis Bouvard on 22nd October respectively. Fourth discovery was made by Pons on 27th November, 1818. Finally, it was J F Encke, who recognised that the comet discovered in 1786, 1795, 1805 and 1818 was the same. He studied the comet religiously and was the first individual who computed its orbit. It was the second comet after Halley’s Comet whose orbit was computed. In recognition of his rigorous efforts, the comet was named after Encke as Comet 2P/ Encke.
Some of the observations made about the comet 2P/ Encke includes:
- It appeared bright and had a faint narrow tail on its first discovery in 1786.
- It could be seen with the naked eye on its second discovery in 1795.
- On its third discovery in 1805, the comet was visible by the naked eye and was similar in size and brightness to the Andromeda Galaxy.
- On its fourth discovery in 1818, it appeared faint. Finally, in 1818–19, J F Encke concluded that this comet had an elliptical orbit.
- The comet had a faint nebula and orbicular or round appearance and its nucleus measured 4.8 km.
- It was observed on 20th April, 2007 by STEREO–A that the tail of the comet was temporarily torn off by magnetic field disturbances that were caused due to coronal mass ejection. However, due to the continuous shedding of dust and gas by the comet, the tail grew back.
Magnitude of the comet 2P/ Encke could be determined only in the 19th century. It was revealed at 4.5 in 1805 and 3.5 in 1829. It was recorded as having a magnitude of about 5.0 during the 1964 apparition. Its brightness was maximum at the magnitude of 6 in 1997 and was about 7 in 2000.
The perihelion distance of the comet 2P/ Encke is noted at 0.3302 AU (nearest to the sun) and its aphelion distance (far from the sun) is noted at 4.11 AU.
The orbital period of the comet 2P/ Encke around the sun is noted at about 3.3 years. This is the shortest orbital period of the periodic comets and is not perturbed by any other major planet.
Comet 2P/ Encke was recovered by the astronomer Carl Ludwig Christian Rumker on 2nd June, 1822 at the Parramatta Observatory, New South Wales and its orbit was calculated by Johann Franz Encke, after whom the comet was named.
Comet 2P/ Encke had experienced one close approach to Mercury, about eleven close approaches to the Earth and two close approaches to Jupiter in the 20th century. However, it is expected to make three close approaches to the Earth and one close approach to the planet Jupiter during the first three decades of the 21st century.
Last apparition of comet 2P/ Encke was on 21st November, 2013 and the next apparition is expected on 10th March, 2017. One of the brightest comets in 2013, it was visible with binoculars, beginning in late September in the evening skies.