Jan Hendrik Oort is a Astronome Dutch (April 28th 1900, Franeker - November 5th 1992, Wassenaar).

He was the director of the Observatoire of Leyde of 1945 with 1970, he undertook many research on our Galaxy. After having highlighted its differential Rotation (1927), it attempted to determine its Masse, by the motion study of the star S and their distribution in the space (1932); it could thus establish its structure in spiral and the duration of its revolution.

It developed, starting from 1950, the theory - today universally allowed - according to which it would exist, with distances from the Sun lain between 40  000 and 100  000 astronomical units, a vast concentration of Comet S (Cloud of Oort). Some of these comets leave sometimes this “cloud” to take a Orbite from which the plan can be different from that of the ecliptic .

Its personality and the importance of its work enabled him to constitute around him a prestigious, in particular in Radioastronomie, known team under the name of school of Leyde. He was president of the international astronomical Union (1958 - 1961) and was allowed in 1953 with the American Academy of Science, like foreign associated member.

The Astéroïde (1691) Oort was named in its honor.