Urbain Jean Joseph Le Verrier (French:[yʁbɛ̃ʒɑ̃ʒozɛfləvɛʁje]; 11 March 1811 – 23 September 1877) was a French astronomer and mathematician who specialized incelestial mechanics and is best known for predicting the existence and position ofNeptune using only mathematics.
The calculations were made to explain discrepancies withUranus'sorbit and thelaws ofKepler andNewton. Le Verrier sent the coordinates toJohann Gottfried Galle in Berlin, asking him to verify. Galle found Neptune the same night he received Le Verrier's letter, within 1° of the predicted position.
Thediscovery of Neptune is widely regarded as a dramatic validation of celestial mechanics, and is one of the most remarkable moments of 19th-century science.
Urbain Le Verrier was born atSaint-Lô, Manche, France, to a modest bourgeois family, his parents being Louis-Baptiste Le Verrier and Marie-Jeanne-Josephine-Pauline de Baudre.[1]
He studied at theÉcole Polytechnique – briefly chemistry, underGay-Lussac, writing papers on the combinations of phosphorus and hydrogen, and of phosphorus and oxygen.[2]
He then switched to astronomy, particularly celestial mechanics, and accepted a job at theParis Observatory. He spent most of his professional life there, eventually becoming director of the institution, from 1854–1870 and again from 1873–1877.[3]
Le Verrier's first work in astronomy was presented to theAcadémie des Sciences in September 1839, entitledSur les variations séculaires des orbites des planètes (On the Secular Variations of the Orbits of the Planets). This work addressed the then most-important question in astronomy: thestability of the Solar System, first investigated byLaplace. He was able to derive some important limits on the motions of the system, but due to the inaccurately-known masses of the planets, his results were tentative.
From 1844 to 1847, Le Verrier published a series of works on periodiccomets, in particular those ofLexell,Faye andDeVico. He was able to show some interesting interactions with the planetJupiter, proving that certain comets were actually the reappearance of previously-known comets flung into different orbits.[4]
Le Verrier's most famous achievement is his prediction of the existence of the then unknown planet Neptune, using only mathematics and astronomical observations of the known planet Uranus. Encouraged by physicistArago,[5] Director of the Paris Observatory, Le Verrier was intensely engaged for months in complex calculations to explain small but systematic discrepancies betweenUranus's observedorbit and the one predicted from thelaws of gravity ofNewton. At the same time, but unknown to Le Verrier, similar calculations were made byJohn Couch Adams in England. Le Verrier announced his final predicted position for Uranus's unseen perturbingplanet publicly to the French Academy on 31 August 1846, two days before Adams's final solution was privately mailed to theRoyal Greenwich Observatory. Le Verrier transmitted his own prediction by 18 September in a letter toJohann Galle of theBerlin Observatory. The letter arrived five days later, and the planet was found with the Berlin Fraunhofer refractor that same evening, 23 September 1846, by Galle andHeinrich d'Arrest within 1° of the predicted location near the boundary betweenCapricorn andAquarius.
There was, and to an extent still is, controversy over the apportionment of credit for the discovery. There is no ambiguity to the discovery claims of Le Verrier, Galle, and d'Arrest. Adams's work was begun earlier than Le Verrier's but was finished later and was unrelated to the actual discovery. Not even the briefest account of Adams's predicted orbital elements was published until more than a month after Berlin's visual confirmation. Adams made full public acknowledgement of Le Verrier's priority and credit (not forgetting to mention the role of Galle) when he gave his paper to the Royal Astronomical Society in November 1846:[6]
I mention these dates merely to show that my results were arrived at independently, and previously to the publication of those of M. Le Verrier, and not with the intention of interfering with his just claims to the honours of the discovery; for there is no doubt that his researches were first published to the world, and led to the actual discovery of the planet by Dr. Galle, so that the facts stated above cannot detract, in the slightest degree, from the credit due to M. Le Verrier.
Early in the 19th century, the methods of predicting the motions of the planets were somewhat scattered, having been developed over decades by many different researchers. In 1847, Le Verrier took on the task to "... embrace in a single work the entire planetary system, put everything in harmony if possible, otherwise, declare with certainty that there are as yet unknown causes of perturbations...",[7] a work which would occupy him for the rest of his life.
Le Verrier began by re-evaluating, to the 7th order, the technique of calculating theplanetary perturbations known as the perturbing function. This derivation, which resulted in 469 mathematical terms, was complete by 1849. He next collected observations of the positions of the planets as far back as 1750. Examining these and correcting for inconsistencies with the most recent data occupied him until 1852.[4]
Le Verrier published, in theAnnales de l'Observatoire de Paris, tables of the motions of all of the known planets, releasing them as he completed them, starting in 1858.[8] The tables formed thefundamental ephemeris of theConnaissance des Temps, the astronomical almanac of theBureau des Longitudes, until about 1912.[9] About that time, Le Verrier's work on the outer planets was revised and expanded byGaillot.[10]
Le Verrier began studying the motion ofMercury as early as 1843, with a report entitledDétermination nouvelle de l'orbite de Mercure et de ses perturbations (A New Determination of the Orbit of Mercury and its Perturbations).[4]In 1859, Le Verrier was the first to report that the slowprecession ofMercury's orbit around theSun could not be completely explained byNewtonian mechanics and perturbations by the known planets. He suggested, among possible explanations, that another planet (or perhaps, instead, a series of smaller 'corpuscules') might exist in an orbit even closer to the Sun than that of Mercury, to account for this perturbation.[11] (Other explanations considered included a slight oblateness of the Sun.) The success of the search forNeptune based on its perturbations of the orbit ofUranus led astronomers to place some faith in this possible explanation, and the hypothetical planet was even namedVulcan. However, no such planet was ever found,[12] and the anomalous precession was eventually explained bygeneral relativity theory.
Le Verrier's methods of management were disliked by the staff of theObservatoire, and the disputes became so great that he was driven out in 1870. He was succeeded byDelaunay, but was reinstated in 1873 after Delaunay accidentally drowned. Le Verrier held the position until his death in 1877.[2]
Le Verrier married Lucille Clotilde Choquet in 1837[13] and had 3 children.[14][15] He died in Paris, France and was buried in theMontparnasse Cemetery. A large stone celestial globe sits over his grave. He will be remembered by the phrase attributed toArago: "the man who discovered a planet with the point of his pen."
^Adams, J.C., MA, FRAS, Fellow of St John's College, Cambridge (1846)."On the Perturbations of Uranus".Appendices to various nautical almanacs between the years 1834 and 1854 (reprints published 1851) (this is a 50Mb download of the pdf scan of the nineteenth-century printed book). UK Nautical Almanac Office, 1851. p. 265. Retrieved23 January 2008.{{cite web}}: CS1 maint: multiple names: authors list (link)
^Lévy, J. (1968). "Trois siècles de mécanique céleste à l'Observatoire de Paris".L'Astronomie (in French).82: 381.Bibcode:1968LAstr..82..381L.
Locher, Fabien (2008),Le Savant et la Tempête. Étudier l'atmosphère et prévoir le temps au XIXe siècle [The Sage and the Tempest. Studying the Atmosphere and Forecasting the Weather in the Nineteenth Century], Carnot (in French), Rennes: Presses Universitaires de Rennes.
