In 1774, Méchain obtained the more permanent post as a calculator with the Depot of the Navy. At that time, he has met Charles Messier, who worked for the same department, but at the small observatory at Hôtel de Clugny. Apparently, the two astronomers became friends around this time.
On the new post, Méchain was first involved in surveys of the French coastline. In addition, he had occasion to make some observations at Versailles. In 1774, he observed an occultation of Aldebaran by the Moon, which he later presented as a memoir to the Academy of Sciences.
In 1777, Pierre Méchain married Barbe-Thérèse Marjou whom he knew from his work in Versailles. They had two sons: Jérôme, born 1780, and Augustin, born 1784, and one daughter.
Like Messier, Pierre Méchain became much devoted to comet observing and hunting, resulting in the original discovery of 8 and independent co-discovery of 3 of these objects (see his discovery list). Also like Messier, he soon started to stumble over nebulous objects, and between 1779 and 1782, discovered the considerable number of 30 deep sky objects, 26 of which were original firsts. As apparently he had got in close cooperation with Charles Messier at that time, he almost instantly communicated his observations to Charles Messier, who usually checked their positions and added them to his catalog. Both astronomers undertook a vigorous effort to find more nebulae between late August 1780 and March 1781, when the manuscript for the final version of the Messier catalog was sent out to print. Méchain's last two contributions, M102 and M103, went into the publication unchecked and without positions.
Four additional findings of Méchain missed the publication; these are now known as M104, M105, M106, and M107. He communicated them to Bernoulli, the editor of the Berliner Astronomisches Jahrbuch, in a letter dated May 6, 1783. As these four objects were not contained in the original Messier catalog, they were longly attributed separately to Pierre Méchain (e.g. by John Herschel and J.L.E. Dreyer, the author of the NGC). In this same letter, Méchain disclaimed - possibly in error - his discovery of M102 as an erroneous re-observation of M101, thereby initiating a still open discussion on the identity of this object.
In this letter, he also mentions the objects listed in Messier's catalog with M97 which are now generally recognized as M108 and M109 after their addition proposed by Owen Gingerich. Moreover, Pierre Méchain states to have observed some more "nebulae" in the region of the Virgo Cluster which Messier had not included in his catalog, but unfortunately doesn't give any detail which could help to identify his presumable discoveries.
There are no noted publications of any later Deep Sky object observations by Pierre Méchain. However, he served as co-editor of the 1795 edition of Jean Fortin's "Atlas Céleste de Flamstéed" (Fortin 1795); on the charts of this work, the positions of many nebulae are given, including those of Méchain's objects M104-M109.
Méchain discovered his first two comets in 1781, and because of his mathematical skills, he was able to calculate their orbits. In particular, he investigated the orbits of the comets of 1532 and 1661, and disproved the then-common hypothesis that this were appearances of the same object. This work won the Grand Prix of 1782 of the Academy of Sciences, and this winning was the main reason that he was made a member of the Academy of Sciences in 1782. Méchain's third comet discovery followed in 1785, and in 1786, he discovered another one which later became famous as "Comet Encke" (after the calculater of its orbit, the German astronomer J.F. Encke). Comet Encke was later independently rediscovered by Caroline Herschel in 1792 and by Pons in 1805, and is the shortest-periodic comet ever discovered, with a period of 3.5 years.
During the 1780s, Méchain undertook several surveys to produce maps, e.g. of Germany and Northern Italy. In 1785, Pierre Méchain became editor of the Connoissance des Temps, the journal which had e.g. published the Messier Catalog - one source states that Charles Messier had been appointed as associate editor in the same year. Méchain was principle editor of the Connoissance des Temps for the years 1788 to 1794 (published 1785 to 1792).
In 1787, Méchain collaborated with J.D. Cassini and Legendre on measuring the acurate longitude difference between Paris and Greenwich. All three visited William Herschel at his observatory in Slough, England in the same year.
Méchain discovered his fifth comet in the same year, 1787. His next, 6th discovery occurred in 1790; this finding was periodic comet Tuttle with a period of 13.75 years, as recognized by Tuttle in 1858.
In 1791, a project was initiated of a new survey of the meridian from Dunkirk to Barcelona, and Méchain undertook the southern part, together with an assistant, Tranchot. The operation started June 25, 1792, suffering from various difficulties caused by the French revolution: At one time, Méchain and Tranchot got arrested by revolutioneers in Essone, who first mistook their instruments as weapons, but later let them proceed.
When in Spain, Méchain got hurt in an accident, and when he had recovered, war had broken out between France and Spain, and he got interned. Nevertheless, he discovered another comet, his 7th, from Barcelona on January 10, 1793. During the terror regime in Paris, while Méchain himself was away, all of his property got lost, and his family suffered greatly. Méchain was eventually allowed to leave Spain for Italy, where he stayed at Genoa for some time, and returned to Paris finally in 1795.
On his return, he became member of the new Academy of Sciences, and the Bureau of Longitudes. Moreover, he was made director of the Paris Observatory, where he discovered his 8th and last comet on December 26, 1799; Messier took part in observing this one in order to obtain its orbit.
Apparently, Méchain was concerned about the quality of the results of his survey, and refused to publish them for a long time. Eventually, he got permission from Napoleon to extend the survey, and left Paris in 1803.
After completing part of this work, Pierre Méchain caught yellow fever and died in Castillion de la Plana in Spain on September 20, 1804.
Pierre Méchain was honored by the astronomical community with the naming (on June 24, 2002) of asteroid (21785) Méchain, discovered by Milos Tichý at Kle on September 21, 1999, and provisionally designated 1999 SS2.
Note that Kenneth Glyn Jones, apparently following Admiral Smyth, has erroneously assigned three more objects to Pierre Méchain: M65, M66, and M68, which actually are all original discoveries of Charles Messier.
M63 1779 Jun 14 [M81] 1779 Aug orig: Bode 1774 Dec 31 [M82] 1779 Aug orig: Bode 1774 Dec 31 M78 1780 Begin [M71] 1780 Jun 28 orig: De Chéseaux 1745-6 M75 1780 Aug 27 M72 1780 Aug 30 M76 1780 Sep 5 M74 1780 Sep End M79 1780 Oct 26 M77 1780 Oct 29 [M80] 1781 Jan 27 orig: Messier 1781 Jan 4 M97 1781 Feb 16 M108 1781 Feb 19 M85 1781 Mar 4 M109 1781 Mar 12 M98 1781 Mar 15 M99 1781 Mar 15 M100 1781 Mar 15 M95 1781 Mar 20 M96 1781 Mar 20 M51B 1781 Mar 20 NGC 5195; companion of M51 M94 1781 Mar 22 M105 1781 Mar 24 M101 1781 Mar 27 M102? 1781 Mar-Apr (NGC 5866) disclaimed by Méchain; still controverse M103 1781 Mar-Apr M104 1781 May 11 M106 1781 Jul M107 1782 AprIn his 1783 letter to Bernoulli, Méchain also states to have found "more nebulae" in the region of the Virgo Cluster but unfortunately doesn't give any detail which could help to identify his presumable discoveries. Therefore, for the time being, these discoveries must be accounted as lost.
Last Modification: April 23, 2013