C/1785 A1 (Messier–Méchain)

Comet Messier–Méchain, also known as C/1785 A1 from its modern nomenclature, is a faint parabolic comet that was observed several times by French astronomers, Charles Messier and Pierre Méchain, in January 1785.

C/1785 A1 (Messier–Méchain)

Discovery[1]
Discovered by	Charles Messier Pierre Méchain
Discovery site	Paris, France
Discovery date	7 January 1785
Designations
Alternative designations	1785 I[2]
Orbital characteristics[3]
Epoch	27 January 1785 (JD 2373045.325)
Observation arc	32 days
Number of observations	9
Perihelion	1.143 AU
Eccentricity	~1.000
Inclination	70.238°
Longitude of ascending node	267.21°
Argument of periapsis	205.63°
Last perihelion	27 January 1785
Physical characteristics[4]
Apparent magnitude	7.5 (1785 apparition)

Discovery and observations

Charles Messier discovered this comet using a small refractor following an observation of Uranus on the night of 7 January 1785.^[1] Approximately 40 minutes later, Pierre Méchain also discovered the same comet from the Paris Observatory.^[4] At the time, the comet was located within the constellation Cetus.^[a]

Messier described the comet as a faint object surrounded by a "central condensation" around it, where he also noted that it became brighter on 9 January than it was two days earlier, but it never became visible to the naked eye.^[4] He continued to observe the comet until 17 January 1785, when it was no longer visible near the star ε Cet.^[5]

Orbit

The only known orbital calculations of the comet were written by Méchain in 1788, where he determined a parabolic trajectory that indicated the comet had reached perihelion on 27 January, while making its closest approach to Earth a day later at a distance of 0.417 AU (62.4 million km)^[4]

In 2012, Maik Meyer noted that the preliminary orbital calculations for the comet C/2012 L2 (LINEAR) were strikingly similar to that of Messier–Méchain, however he concluded that this is only a coincidence rather than a return of C/1785 A1 itself.^[6]