Oort cloud

Oort cloud

[awrt, ohrt]
noun Astronomy.
a region of the solar system far beyond the orbit of the dwarf planet Pluto in which billions of comets move in nearly circular orbits unless one is pulled into a highly eccentric elliptical orbit by a passing star. Compare Kuiper belt.

Origin:
1975–80; after Dutch astronomer Jan Hendrik Oort (1900–1992), who proposed its existence

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Based on the Random House Dictionary, © Random House, Inc. 2014.
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Etymonline
Word Origin & History

Oort cloud
in reference to the hypothetical cloud of small objects beyond Pluto that become comets, proposed 1949 by Du. astronomer Jan Hendrick Oort (1900-1992), and named for him by 1968.
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Science Dictionary
Oort cloud   (ôrt)  Pronunciation Key 
A sphere-shaped mass of more than 100 billion comets that makes up the outer edge of the solar system, surrounding the Kuiper belt and the planets. Some comets from this area are drawn into the inner solar system by passing stars and other forces and take more than 200 years to make one complete orbit of the Sun. Compare Kuiper belt.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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