1691 Oort (1956 RB) is a main-belt asteroid discovered on September 9, 1956 by Ingrid van Houten-Groeneveld and Karl Wilhelm Reinmuth at Heidelberg. It was named after the Dutch astronomer Jan Oort.

Jan Hendrik Oort FRS[1] (Franeker, 28 April 1900 – Leiden, 5 November 1992) was a Dutch astronomer. He was a pioneer in the field of radio astronomy. 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 (the Westerbork Synthesis Radio 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.

His hypothesis that the comets have a common origin, postulated in 1950, was later proven to be incorrect in detail, though correct in principle. That is, different types of comets have origins in different regions of the outer solar system. For more, see Oort Cloud, Hills Cloud, and Kuiper Belt. Another contribution Oort made was to demonstrate that the light from the Crab nebula was polarized.

Professor Oort was elected an honorary member of the Royal Astronomical Society of Canada on 1954-01-19.

Orbit type: Main Belt Asteroid