Pierre François André Méchain was a French astronomer and surveyor who, with Charles Messier, was a major contributor to the early study of deep-sky objects and comets.
Pierre Mechain, a French astronomer and hydrographer who, with Jean Delambre, measured the meridian arc from Dunkirk, Fr., to Barcelona. The measurement was made between 1792 and 1798 to establish a basis for the unit of length in the metric system called for by the French national legislature. Mechain also discovered 11 comets and calculated the orbits of these and other known comets.
Pierre Méchain was born in Laon, the son of the ceiling designer and plasterer Pierre François Méchain and Marie–Marguerite Roze. He displayed mental gifts in mathematics and physics but had to give up his studies for lack of money. However, his talents in astronomy were noticed by Jérôme Lalande, for whom he became a friend and proof-reader of the second edition of his book “L’Astronomie”. Lalande then secured a position for him as assistant hydrographer with the Naval Depot of Maps and Charts at Versailles, where he worked through the 1770s engaged in hydrographic work and coastline surveying. It was during this time—approximately 1774—that he met Charles Messier, and apparently, they became friends. In the same year, he also produced his first astronomical work, a paper on an occultation of Aldebaran by the Moon and presented it as a memoir to the Academy of Sciences. Mechain early in life showed mathematical prowess and worked as a hydrographer for the Naval Map Archives at Versailles during the 1770s.He turned to astronomy, and in 1782 his work with comets won him admission to the Académie Royale des Sciences. In addition, Mechain discovered numerous nebulae that were later incorporated by Charles Messier into his famous catalog of clusters and nebulae.
He participated in the Anglo-French Survey (1784–1790) to measure by trigonometry the precise distance between the Paris Observatory and the Royal Greenwich Observatory. This project was initiated by Dominique, comte de Cassini, and in 1787 Méchain visited Dover and London with Cassini and Adrien-Marie Legendre to facilitate its progress. The three men also visited the astronomer William Herschel at Slough. With his surveying skills, he worked on maps of Northern Italy and Germany after this, but his most important mapping work was geodetic: the determination of the southern part of the meridian arc of the Earth’s surface between Dunkirk and Barcelona beginning in 1791.