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Polyaenus

(Encyclopedia)Polyaenus pŏlˌē-ēˈnəs [key], fl. c.153, Macedonian Greek writer. His Stratagems, anecdotes on the ruses of war, takes much from various ancient sources now lost. ...

Roman art

(Encyclopedia)Roman art, works of art produced in ancient Rome and its far-flung provinces. The continued striving after three-dimensional illusionist effects revealed in the various phases of painting was dup...

Hubble Space Telescope

(Encyclopedia)Hubble Space Telescope (HST), the first large optical orbiting observatory. Built from 1978 to 1990 at a cost of $1.5 billion, the HST (named for astronomer E. P. Hubble) was expected to provide the c...

Iapetus, in astronomy

(Encyclopedia)Iapetus īăpˈĭtəs [key], in astronomy, one of the named moons, or natural satellites, of Saturn. Also known as Saturn VIII (or S8), Iapetus is 907 mi (1460 km) in diameter, orbits Saturn at a mean...

Omar Khayyam

(Encyclopedia)Omar Khayyam kīämˈ [key], fl. 11th cent., Persian poet and mathematician, b. Nishapur. He was called Khayyam [tentmaker] probably because of his father's occupation. The details of his life are mos...

Roche limit

(Encyclopedia)Roche limit, the closest distance that a celestial body held together only by its own gravity can come to a planet without being pulled apart by the planet's tidal (gravitational) force. This distance...

Tombaugh, Clyde William

(Encyclopedia)Tombaugh, Clyde William tŏmˈbô [key], 1906–97, American astronomer, b. Streator, Ill. Although lacking formal training or a college degree, he was hired in 1929 as an assistant by the Lowell Obse...

celestial mechanics

(Encyclopedia)celestial mechanics, the study of the motions of astronomical bodies as they move under the influence of their mutual gravitation. Celestial mechanics analyzes the orbital motions of planets, dwarf pl...

Ricci, Matteo

(Encyclopedia)Ricci, Matteo mät-tāˈō rētˈchē [key], 1552–1610, Italian missionary to China. He entered the Society of Jesus, and in Rome he studied under Clavius. Ricci was sent to the Indies (1578), and h...

Alcamo

(Encyclopedia)Alcamo älˈkämō [key], city, NW Sicily, Italy. It is an agricultural and industrial center and is noted for its white wine. The ruins of the ancient Greek settlement of...