An Etymological Dictionary of Astronomy and Astrophysics

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.

See also: 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.