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Definition: Pluto (astronomy) from The Macmillan Encyclopedia

The smallest and usually outermost planet, orbiting the sun every 248 years at a mean distance of 5900 million km. Its eccentric orbit has brought it inside Neptune's orbit for the period 1979-99. Pluto was discovered in 1930 but little was known about it until its satellite was discovered in 1978. It is a very cold low-density body about 3000 km in diameter.

Pluto

From The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide
Dwarf planet. Until its reclassification in 2006 it was considered to be the smallest and, usually, outermost planet of the Solar System. The existence of Pluto was predicted by calculation by US astronomer Percival Lowell and located by US astronomer Clyde Tombaugh in 1930. Its highly elliptical orbit occasionally takes it within the orbit of Neptune, as in 1979–99. Pluto has a mass about 0.002 of that of Earth. Mean distance from the Sun 5.8 billion km/3.6 billion mi Equatorial diameter 2,300 km/1,438 mi Rotation period 6.39 Earth days Year 248.5 Earth years Atmosphere thin atmosphere with small amounts of methane gas Surface low density, composed of rock and ice, primarily frozen methane; there is an ice cap at Pluto's north pole Satellites one moon, Charon Charon, Pluto's largest moon, was discovered in 1978 by US astronomer James Christy. It is about 1,200 km/750 mi in diameter, half the size of Pluto. It orbits about 20,000 km/12,500 mi from the planet's centre every 6.39 days – …
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Full text Article Pluto

From Astronomy Encyclopedia
Pluto Pluto (left) and its satellite Charon...
Ninth and smallest planet in the Solar System. It is slightly smaller than Neptune's largest satellite, TRITON , with which it may have much in common. The realization that Pluto is much smaller than originally assumed, together with the fact that it shares many properties with EDGEWORTH - KUIPER…
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Full text Article Pluto

From Philip's Encyclopedia
Smallest and outermost planet of the Solar System. Independently, William H. Pickering and Percival Lowell calculated its possible existence. The planet was located (1930) by Clyde Tombaugh - within 5° of Lowell's predicted position. Pluto has a mottled surface with light and dark regions, and signs…
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Full text Article Pluto

From Brewer's Dictionary of Modern Phrase and Fable
The ninth planet in the solar system was discovered only in 1930 by the American astronomer Clyde W. Tombaugh during a systematic search for a planet beyond Neptune, itself discovered in 1846. Tombaugh recognized the new planet in a series of photographs he had taken at the Lowell Observatory at…
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Full text Article Pluto

From Encyclopedia of the History of Astronomy and Astrophysics Full text Article The solar system Full text Article Smaller objects
The orbits of the August Meteors or...
Urbain Le Verrier speculated on the possible existence of planets further from the Sun than Neptune within a week of Neptune's discovery in 1846. Some thirty years later, David P. Todd analysed Uranus’ orbit and concluded that it was being affected by a trans-Neptunian planet, but his search for it…
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The Pluto System. This Hubble Space...
Abstract Pluto is the prototype of the dwarf planets so common in the Kuiper Belt and beyond. It is in an elliptical, 248year orbit that ranges from 29.6 to 48.8 astronomical units (AU) from the Sun. Its largest satellite, Charon, is close enough to Pluto in size that the pair is widely considered…
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Full text Article Pluto

From The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide
Dwarf planet. Until its reclassification in 2006 it was considered to be the smallest and, usually, outermost planet of the Solar System. The existence of Pluto was predicted by calculation by US astronomer Percival Lowell and located by US astronomer Clyde Tombaugh in 1930. Its highly elliptical…
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Full text Article Pluto

From Collins Dictionary of Astronomy
The ninth and smallest planet of the Solar System, discovered in 1930 by Clyde Tombaugh at the Lowell Observatory in Arizona. Its 248.59 year orbit has a higher inclination to the ecliptic (17.1°) and a greater eccentricity (0.25) than any other planet. Although it has the greatest mean planetary…
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Full text Article Pluto

From Science Encyclopedia: Encyclopedia of Space and Astronomy
Pluto, a dwarf planet, has remained a mystery since its discovery by the American astronomer Clyde Tombaugh (1906–97) in 1930. It was labeled as a planet until 2006, when it was given the status of dwarf planet. Pluto has yet to be viewed close-up by spacecraft, and given its great distance from the…
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Full text Article Pluto

From Brewer's Dictionary of Phrase and Fable
In Greek mythology, one of the titles of hades , the ruler of the underworld, the kingdom of the dead. His Greek name Ploutōn meant literally ‘wealth-giver’, wealth being seen as coming out of the earth. The dwarf planet called Pluto was discovered only in 1930 by the US astronomer Clyde W. Tombaugh…
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Full text Article Pluto

From The New Dictionary of Cultural Literacy, Houghton Mifflin
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 ) Astronomers in the late nineteenth century, thinking they saw disturbances in the orbits of Uranus and Neptune , …
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