Pierre Méchain | |
|---|---|
 Portrait of Méchain, c. 1882 | |
| Born | Pierre François André Méchain (1744-08-16)16 August 1744 Laon, France |
| Died | 20 September 1804(1804-09-20) (aged 60) Castellón de la Plana, Spain |
| Known for | Deep-sky objects comets metre |
| Scientific career | |
| Fields | astronomy |
| Institutions | Paris Observatory |
Pierre François André Méchain (French pronunciation:[pjɛʁfʁɑ̃swaɑ̃dʁemeʃɛ̃]; 16 August 1744 – 20 September 1804) was a Frenchastronomer andsurveyor who, withCharles Messier, was a major contributor to the early study ofdeep-sky objects andcomets.
Pierre Méchain was born inLaon in northern France, the son of the ceiling designer and plasterer Pierre François Méchain and Marie–Marguerite Roze. He displayed mental gifts inmathematics andphysics but had to give up his studies for lack of money. However, his talents inastronomy were noticed byJérôme 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 atVersailles, where he worked through the 1770s engaged inhydrographic work and coastline surveying. It was during this time—approximately 1774—that he metCharles Messier, and apparently, they became friends. In the same year, he also produced his first astronomical work, a paper on an occultation ofAldebaran by theMoon, and presented it as a memoir to the Academy of Sciences.
In 1777, 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. He was admitted to the FrenchAcadémie des sciences in 1782, and was the editor ofConnaissance des Temps from 1785 to 1792; this was the journal which, among other things, first published the list ofMessier objects. In 1789 he was elected aFellow of the Royal Society.[1]
Méchain participated in theAnglo-French Survey (1784–1790) to measure bytrigonometry the precise distance between theParis Observatory and theRoyal Greenwich Observatory. This project had been initiated byCésar-François Cassini de Thury, who died in 1784, and in 1787 Méchain visited Dover and London with Cassini de Thury’s sonDominique, comte de Cassini andAdrien-Marie Legendre to facilitate its progress. The three men also visited the astronomerWilliam Herschel atSlough, who had discoveredUranus in 1781.
With his surveying skills, Méchain worked on maps of Northern Italy and Germany after this, but his most important mapping work wasgeodetic: the determination of the southern part of themeridian arc of theEarth's surface betweenDunkirk andBarcelona beginning in 1791. This measurement would become the basis of themetric system's unit of length, the meter. He encountered numerous difficulties on this project, largely stemming from the effects of theFrench Revolution. He was arrested after it was suspected his instruments were weapons, he was interned in Barcelona after war broke out between France and Spain, and his property in Paris was confiscated duringThe Terror. He was released from Spain to live in Italy, then returned home in 1795.
A particularly intriguing fact about this project was that Méchain was uncertain of the precision of his measurements owing to anomalous results in verifying his latitude by astronomical observation. Ultimately, the distance from the pole to the equator, which Méchain and his associateJean Baptiste Joseph Delambre had intended to be exactly ten million meters (or ten thousand kilometres), was determined in the late 20th century by space satellites to be 10,002,290 metres.[2] This small error of 2,290 metres equals 1.423 statute miles; the error in such a large measurement amounts to 14½ inches per statute mile. It represents in each metre an error of approximately 0.23 millimetres[3] – slightly more than the width of a single strand of human hair. This discrepancy is sometimes mentioned as "Méchain's error", with the suggestion that the tiny variation in the length of the meridian (not detected for nearly two hundred years) can be attributed to Méchain's calculations. But analysis of Méchain's figures reveals that Méchain consistently kept the discrepancy very tiny, essentially forcing his individual reported measurements to appear more precise and consistent than would be reasonably expected of a survey involving more than a hundred measurements of mostly rough country using 18th-century equipment; Méchain's putative error did not affect the final value of the length of the metre nor the measurement of the meridian.[4]
From 1799, Méchain was the director of theParis Observatory.
Continuing doubts about his measurements of the Dunkirk-Barcelona arc led him to return to that work. This took him back to Spain in 1804, where he caughtyellow fever and died inCastellón de la Plana.
Méchain discovered either 25 or 26 deep-sky objects, depending on how one countsM102. Méchain disavowed the M102 observation in 1783, claiming it was a mistaken re-observation of M101. Since that time, others have proposed that he did in fact observe another object, andsuggested what they might be.
Open cluster Globular cluster Nebula Planetary nebula Supernova remnant Galaxy Other
| Messier number | NGC/IC Number | Common name | Date of Discovery | Object type | Distance (kly) | Constellation | Apparent magnitude |
|---|---|---|---|---|---|---|---|
| M63 | NGC 5055 | Sunflower Galaxy | 14 June 1779 | Galaxy, spiral | 37,000 | Canes Venatici | 8.5 |
| M72 | NGC 6981 | 30 August 1780 | Cluster, globular | 53 | Aquarius | 10.0 | |
| M74 | NGC 628 | Sep 1780 | Galaxy, spiral | 35,000 | Pisces | 10.5 | |
| M75 | NGC 6864 | 27 August 1780 | Cluster, globular | 58 | Sagittarius | 9.5 | |
| M76 | NGC 650, NGC 651 | Little Dumbbell Nebula | 5 September 1780 | Nebula, planetary | 3.4 | Perseus | 10.1 |
| M77 | NGC 1068 | Cetus A | 29 October 1780 | Galaxy, spiral | 60,000 | Cetus | 10.5 |
| M78 | NGC 2068 | Begin 1780 | Nebula, diffuse | 1.6 | Orion | 8.0 | |
| M79 | NGC 1904 | 26 October 1780 | Cluster, globular | 40 | Lepus | 8.5 | |
| M85 | NGC 4382 | 4 March 1781 | Galaxy, lenticular | 60,000 | Coma Berenices | 10.5 | |
| M94 | NGC 4736 | 22 March 1781 | Galaxy, spiral | 14,500 | Canes Venatici | 9.5 | |
| M95 | NGC 3351 | 20 March 1781 | Galaxy, barred spiral | 38,000 | Leo | 11.0 | |
| M96 | NGC 3368 | 20 March 1781 | Galaxy, spiral | 38,000 | Leo | 10.5 | |
| M97 | NGC 3587 | Owl Nebula | 16 February 1781 | Nebula, planetary | 2.6 | Ursa Major | 9.9 |
| M98 | NGC 4192 | 15 March 1781 | Galaxy, spiral | 60,000 | Coma Berenices | 11.0 | |
| M99 | NGC 4254 | 15 March 1781 | Galaxy, spiral | 60,000 | Coma Berenices | 10.5 | |
| M100 | NGC 4321 | 15 March 1781 | Galaxy, spiral | 60,000 | Coma Berenices | 10.5 | |
| M101 | NGC 5457 | Pinwheel Galaxy | 27 March 1781 | Galaxy, spiral | 27,000 | Ursa Major | 7.9 |
| M102 | (Not conclusively identified) | ||||||
| M103 | NGC 581 | Mar–Apr 1781 | Cluster, open | 8 | Cassiopeia | 7.0 |
He independently discovered four others, originally discovered by someone else but unknown to him at the time and included in the Messier catalogue:M71, discovered byJean-Philippe de Chéseaux in the 1740s;M80, discovered by Messier about two weeks earlier than Méchain's observation; andM81 andM82, discovered originally byJohann Bode.
Six other discoveries are "honorary Messier objects" added to the list in the 20th century:
| Messier number | NGC/IC Number | Common name | Date of Discovery | Object type | Distance (kly) | Constellation | Apparent magnitude |
|---|---|---|---|---|---|---|---|
| M104 | NGC 4594 | Sombrero Galaxy | 11 May 1781 | Galaxy, spiral | 50,000 | Virgo | 9.5 |
| M105 | NGC 3379 | 24 March 1781 | Galaxy, elliptical | 38,000 | Leo | 11.0 | |
| M106 | NGC 4258 | Jul 1781 | Galaxy, spiral | 25,000 | Canes Venatici | 9.5 | |
| M107 | NGC 6171 | Cluster, globular | 20 | Ophiuchus | 10.0 | ||
| M108 | NGC 3556 | 19 February 1781 | Galaxy, barred spiral | 45,000 | Ursa Major | 11.0 | |
| M109 | NGC 3992 | 12 March 1781 | Galaxy, barred spiral | 55,000 | Ursa Major | 11.0 |
He also discoveredNGC 5195, the companion galaxy that makes M51 (theWhirlpool Galaxy) so distinctive.
Méchain never set out to observe deep-sky objects. Like Messier, he was solely interested in cataloguing objects that might be mistaken forcomets; having done so, he was the second-most successful discoverer of comets of his time, after Messier himself.
All together, he originally discovered eight comets, and co-discovered three.[5]
His sole discoveries are:
Méchain's co-discoveries are:
Note that only the two named comets have been connected to periodic comets that have computed orbits and in neither case was he an observer when they were computed, so by that technical definition (commonly used for comets since the 19th century) Méchain did not discover any of these nine.
On 24 June 2002,Asteroid21785 Méchain was named in his honour, discovered byMiloš Tichý atKleť Observatory on 21 September 1999, and provisionally designated 1999 SS2.
