An Etymological Dictionary of Astronomy and Astrophysics
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A huge theoretical cloud of → comets surrounding the Sun between about 50,000 and 100,000 → astronomical units and thought to be the reservoir of → long-period comets entering the inner solar system.

Named after Jan Hendrik Oort (1900-1992), a Dutch astronomer who proposed its existence in 1950. He also made major contributions to our knowledge of the structure and rotation of the Milky Way Galaxy; → cloud.