Comets, Cloud of

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Comets, Cloud of

 

(Oort’s cloud of comets), a hypothetical invisible swarm of comets extending to the farthest reaches of the solar system (the aphelia of certain comets measure 50,-000–150,000 astronomical units), where the gravitational force of the sun is comparable in magnitude to the total gravitational field of the Milky Way Galaxy. The hypothesis was proposed by the Dutch astronomer J. Oort in 1950. Perturbations caused by the stars nearest to the sun change the orbits of members of the cloud of comets, carrying some of them into orbits with perihelia near the sun. Under these conditions the comets can be observed.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.