Oort, Jan Hendrik

Oort, Jan Hendrik (ōrt), 1900–1992, Dutch astronomer. He confirmed (1927) Bertil Lindblad's theory of the Milky Way galaxy's rotation. In the 1950s he and his colleagues used radio astronomical means to map the spiral-arm structure of the galaxy. Oort proposed (1950) that comets originate in a cloud of material (the

Oort cloud) orbiting the sun at great distance and that they are occasionally deflected into the inner solar system by gravitational perturbation from the passing of nearby stars.

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Oort, Jan Hendrik 

Born Apr. 28, 1900, in Franeker. Dutch astronomer. Professor at the University of Leiden (1935).

In 1924, Oort began working at the Leiden Observatory, and from 1945 to 1970 he was its director. He is primarily involved in the study of stellar motion. In 1927 he proposed formulas for the detection of the differential rotation of the Milky Way Galaxy by observing the radial velocities and proper motions of the stars; applying his formulas, he demonstrated the rotation of the galaxy. In 1938 he proposed a method for determining the spatial density distribution of the stars. He also worked on problems involving the structure of the interstellar medium and the Milky Way Galaxy using cosmic radio-emission data. From 1935 to 1948 he was secretary-general and from 1958 to 1961 president of the International Astronomical Union. He is a foreign member of the Academy of Sciences of the USSR (1966).

WORKS

“Investigations Concerning the Rotational Motion of the Galactic System.” Bulletin of the Astronomical Institutes of the Netherlands, 1927, vol. 4.
“Dynamics of the Galactic System in the Vicinity of the Sun.” Ibid., 1928, vol. 4.
“Absorption and Density Distribution in the Galactic System.” Ibid., 1938, vol. 8.