Charles Eugène Delaunay was an French astronomer, mathematician and scientist whose theory of lunar motion advanced the development of planetary-motion theories.
Background
Charles Eugène Delaunay was born on April 9, 1816, in Lusigny-sur-barse, Champagne-Ardenne, France. Delaunay’s father, Jacques-Hubert, was a surveyor who later bought the office of bailiff. His mother, Catherine, was the daughter of a farmer. Delaunay was very close to his mother as a young child and remained so throughout his life.
In 1818, when Delaunay was two years old, his father acquired the office of a bailiff in Ramerupt, which is about 20 km northeast of Troyes. When he was still young Delaunay was sent to Troyes to live with one of his uncles who was a manual worker.
Education
Delaunay was a bright pupil in secondary school at Troyes, he showed such a gift for mathematics that he was admitted to the École Polytechnique in 1834 and graduated in 1836, first in his class.
Mme la Marquise de Laplace donated a new annual prize, the Laplace Prize, to be given to the student who was ranked top in his year at the École Polytechnique. Delaunay had graduated before the prize was instituted but Mme de Laplace requested that he become the first recipient of the prize which consisted of the complete works of Laplace. It turned out to be a decision which changed the course of Delaunay's career, for reading Laplace's great works gave him a passion for celestial mechanics and he decided that he would make a career in that subject. Mme la Marquise de Laplace was delighted with the first winner of the prize and she called him "her eldest son".
Arago suggested to Delaunay that he come to the Paris Observatory and train to become an astronomer but Savary advised against this course of action. Delaunay then entered the École des Mines and trained as an engineer.
Delaunay then studied under Jean-Baptiste Biot at the Sorbonne. For his doctoral dissertation Delaunay undertook research on the calculus of variations and was awarded his doctorate for his thesis De la distinction des maxima et des minima dans les questions qui dépendent de la méthode des variations in 1841.
Although Delaunay was by assignment a mining engineer, he served in various engineering schools and at the University of Paris as professor of mechanics, mathematics, or astronomy. His first researches were on calculus of variations, on perturbations of Uranus (1842), and on the theory of tides (1844). Delaunay’s work in lunar theory started in the 1840s. He published the principle of what is known as the Delaunay method in 1846 and generalized it in 1855.
The Delaunay method, further developed by Anders Lindstedt, Poincaré, and Hugo von Zeipel, was a major contribution to analytical mechanics. It consists of a single procedure permitting elimination from the system of canonical equations, one by one, of all the terms of the disturbing function and hence the building up, term by term, of the solution of the problem. Delaunay applied his method to the moon, computing all the terms up to the seventh order and some additional ones of the eighth and ninth orders. This work was published in 1860 and 1867.
It is noteworthy that, in studying the incompatibility between the observed and the computed values of the secular acceleration of the moon, Delaunay suggested that it could be caused by a slowing of the rotation of the earth by tidal friction (1865). This hypothesis is now known to be correct.
He was appointed director of the Paris observatory in March 1870, after Le Verrier, in a dispute with the staff, was dismissed. But in the two years before his death Delaunay had to devote all his efforts to trying to save the observatory during the Franco-Prussian War and the Commune.
Charles Eugène Delaunay went down in history as a noted astronomer and mathematician whose lunar motion studies were important in advancing both the theory of planetary motion and mathematics.
Crater Delaunay was named in his honor.
He is one of the 72 scientists commemorated on the Eiffel Tower.
Delaunay was a member of the Academie des Sciences (1855), the Bureau des Longitudes (1862), and the Royal Society (1869).
The Academie des Sciences
,
France
1855
The Bureau des Longitudes
,
France
1862
The Royal Society
,
France
1869
Personality
There was a long-time rivalry between Delaunay and Le Verrier. Delaunay recognized his colleague’s scientific achievements but fought his dictatorial rule over astronomical research.
Connections
Delaunay married Marie-Olympe Millot in 1839, and they had a son the following year.
Father:
Jacques-Hubert Delaunay
Mother:
Catherine (Choiselat) Delaunay
Spouse:
Marie-Olympe (Millot) Delaunay
colleague:
Urbain Le Verrier
Urbain Jean Joseph Le Verrier was a French astronomer and mathematician who specialized in celestial mechanics.
