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brown dwarf

(Encyclopedia)brown dwarf, in astronomy, celestial body that is larger than a planet but does not have sufficient mass to convert hydrogen into helium via nuclear fusion as stars do. Also called “failed stars,”...

Terminus

(Encyclopedia)Terminus tûrˈmĭnəs [key], in ancient Rome, both the boundary markers between properties and the name of the god who watched over boundaries. Property lines were of great importance, particularly t...

Lagrange, Joseph Louis, Comte

(Encyclopedia)Lagrange, Joseph Louis, Comte zhôzĕfˈ lwē kôNt lägräNzhˈ [key], 1736–1813, French mathematician and astronomer, b. Turin, of French and Italian descent. Before the age of 20 he was professor...

Jovian planets

(Encyclopedia)Jovian planets, the planets Jupiter, Saturn, Uranus, and Neptune. They are all larger and more massive than the earth. Since they rotate faster, they are more flattened at the poles than are the terre...

satellite, natural

(Encyclopedia)satellite, natural, celestial body orbiting a planet, dwarf planet, asteroid, or star of a larger size. The most familiar natural satellite is the earth's moon; thus, satellites of other planets are o...

Young, Charles Augustus

(Encyclopedia)Young, Charles Augustus, 1834–1908, American astronomer, b. Hanover, N.H., grad. Dartmouth, 1853. He discovered the reversing layer of the solar atmosphere and proved the gaseous nature of the sun's...

Cassini

(Encyclopedia)Cassini käs-sēˈnē [key], name of a family of Italian-French astronomers, four generations of whom were directors of the Paris Observatory. Gian Domenico Cassini, 1625–1712, was born in Italy and...

Lemonnier, Pierre Charles

(Encyclopedia)Lemonnier, Pierre Charles pyĕr shärl ləmônyāˈ [key], 1715–99, French astronomer. For many years he was professor of physics at the Collège de France. He studied the moon and the influence of ...

space probe

(Encyclopedia)space probe, space vehicle carrying sophisticated instrumentation but no crew, designed to explore various aspects of the solar system (see space exploration). Unlike an artificial satellite, which is...

Thor

(Encyclopedia)Thor dōˈnär [key], Norse god of thunder. An ancient and highly revered divinity, Thor was the patron and protector of peasants and warriors. As a god of might and war he was represented as extremel...