Jan Oort

Jan Oort (1900-1992), Dutch astronomer, noted for his determination that the earth's galaxy, the Milky Way, rotates, and for his contributions to comet theory. Born in Franeker, Jan Hendrik Oort was educated at the University of Groningen. Associated with the Leiden University and its observatory, Oort, with his colleagues, established the Milky Way's rotation in the 1920s; they also worked out the mass of the galaxy and the distance of its center from the sun. Oort pioneered in Dutch radio astronomy. He proposed in 1950 that a cloud of cometary material surrounds the solar system at an enormous distance, a concept now generally accepted.