Jan Hendrik Oort (April 28, 1900 – November 5, 1992) was an internationally famous Dutch astronomer. He profoundly stimulated radio astronomy. The well-known Oort cloud bears his name.

Oort was born in Franeker in Friesland and studied in Groningen with Jacobus Cornelius Kapteyn. His Ph.D thesis was titled The stars of high velocity. In 1927 he proved that the Milky Way galaxy rotates, by analyzing the movements of stars. In 1935 he became professor at Leiden University at the faculty where Ejnar Hertzsprung was the director.

Oort was fascinated by radio waves from the universe. After the Second World War he was a pioneer in the new field of radio astronomy, using an old radar antenna from the Germans.

In the 1950s he raised funds for a new radio telescope in Dwingeloo, in the east part of the Netherlands, to research the centre of the galaxy. In 1970 a bigger telescope (the Westerbork Synthesis Radio Telescope) was built in Westerbork, near the old one. It consisted of twelve smaller telescopes working together as an interferometer to perform aperture synthesis observations, a technique which had been previously suggested by Oort, but which was first tested experimentally in Cambridge by Martin Ryle and in Sydney by Joseph Pawsey .

His hypothesis that the comets have a common origin, postulated in 1950, was later proven to be correct. Another contribution of Oort was that he was able to demonstrate that the light from the Crab nebula was polarized.

Honors

• Bruce Medal in 1942
• Gold Medal of the Royal Astronomical Society in 1946
• Henry Norris Russell Lectureship in 1951