April 9, 1816 – August 5, 1872
Charles Delaunay was a French astronomer and mathematician. His lunar motion studies were important in advancing both the theory of planetary motion and mathematics.
Born in Lusigny-sur-Barse, France, Delaunay studied under Jean-Baptiste Biot at the Sorbonne. He worked on the mechanics of the Moon as a special case of the three-body problem. He published two volumes on the topic, each of 900 pages in length, in 1860 and 1867. The work hints at chaos in the system, and clearly demonstrates the problem of so-called "small denominators" in perturbation theory. His infinite series expression for finding the position of the Moon converged too slowly to be of practical use but was a catalyst in the development of functional analysis.
Delaunay became director of the Paris Observatory in 1870 but drowned in a boating accident near Cherbourg, France two years later.
Delaunay was a member of the Académie des Sciences, (1855) and was awarded the Gold Medal of the Royal Astronomical Society, (1870).
The Lunar crater Delaunay is named in his honor.