Cultural Dictionary

Pluto definition

The Roman name of Hades, the Greek and Roman god of the underworld and ruler of the dead.

Note: The planet Pluto is usually the most distant planet in the solar system.
American Heritage
Cultural Dictionary

Pluto definition

In astronomy, the smallest of the major planets, usually ninth from the sun. Pluto was discovered in 1930 and is named for the Roman god of the underworld. (See solar system)

Note: Astronomers in the late nineteenth century, thinking they saw disturbances in the orbits of Uranus and Neptune, suspected that there was a ninth planet, not yet discovered, exerting gravitation on the other two. In the early twentieth century, astronomers searched for that planet and found Pluto. Ironically, Pluto is much too small to be the planet they sought.
Note: Pluto's orbit is a stretched ellipse, unlike the orbits of the other major planets, which are nearly circular. As a result, for a period ending in 1999, Pluto was actually closer to the sun than Neptune.
Note: There is some debate among astronomers as to whether Pluto should really be classified as a planet or should instead be considered a large asteroid-like body.
The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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