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Jan Hendrik Oort ForMemRS was a prolific Dutch astronomer. He made many important contributions in the field of astronomy and was a pioneer in the field of radio astronomy. In 1932 he became the first person to discover evidence of dark matter. First proposed by Swiss astronomer Fritz Zwicky in the 1930s, at nearly the same time, Jan Oort in the Netherlands discovered that the density of matter near the Sun was nearly twice what could be explained by the presence of stars and gas alone. The Oort cloud of comets bears his name.
Oort was born in Franeker, Friesland and studied in Groningen with Jacobus Cornelius Kapteyn. His Ph.D thesis was titled The stars of high velocity. In 1927 he confirmed Bertil Lindblad's theory that the Milky Way galaxy rotates, by analyzing the movements of stars. In 1935 he became professor at the observatory of the University of Leiden, where Ejnar Hertzsprung was the director. Oort was fascinated by radio waves from the universe. After the Second World War he began work 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 center of the galaxy. In 1970 a bigger telescope was built in Westerbork, near the old one. It consisted of twelve smaller telescopes working together to perform radio interferometry 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.
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