Charles-Eugène Delaunay (April 9, 1816 – August 5, 1872) was a French astronomer and mathematician.

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. 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.

He won the Gold Medal of the Royal Astronomical Society in 1870.

Delaunay became director of the Paris Observatory in 1870 but was drowned in a boating accident near Cherbourg, France two years later.

Publications

• Cours élémentaire de mécanique (1850)
• Traité de mécanique rationnelle (1856)
• La Théorie du mouvement de la lune, 2 vols (1860-7)