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equator

(Encyclopedia)equator, imaginary great circle around the earth, everywhere equidistant from the two geographical poles and forming the base line from which latitude is reckoned. The equator, which measures c.24,902...

geomorphology

(Encyclopedia)geomorphology, study of the origin and evolution of the earth's landforms, both on the continents and within the ocean basins. It is concerned with the internal geologic processes of the earth's crust...

tektite

(Encyclopedia)tektite tĕktīt [key], naturally occurring, silica-rich (65%–80% SiO2) glass resembling obsidian and sometimes shale, and is normally jet black to olive green. They appear as small rounded or elong...

space exploration

(Encyclopedia)CE5 Moon mission assembly CE5 Stages in a moon mission shown counterclockwise from launching on the first day to splashdown on the ninth day. space exploration, the investigation of physical co...

Bradley, James

(Encyclopedia)Bradley, James, 1693–1762, English astronomer. His discovery of the aberration of light, announced in 1728, provided an important line of evidence for the motion of the earth around the sun. In 1742...

Uranus , in Greek religion and mythology

(Encyclopedia)Uranus, in Greek religion and mythology, the heaven, first ruler of the universe, son of Gaea (the earth). He was the father of Gaea's children, the Titans, the Cyclopes, and the Hundred-handed Ones (...

quadrature

(Encyclopedia)quadrature, in astronomy, arrangement of two celestial bodies at right angles to each other as viewed from a reference point. If the reference point is the earth and the sun is one of the bodies, a pl...

comet

(Encyclopedia)CE5 Comet: Whatever the direction of a comet's flight, its “tail” always points away from the sun. The tail disappears when the comet is far from the sun. comet [Gr.,=longhaired], a small cele...

Yom Kippur

(Encyclopedia)Yom Kippur [Heb.,=day of atonement], in Judaism, the most sacred holy day, falling on the 10th day of the Jewish month of Tishri (usually late September or early October). It is a day of fasting and p...

Ptolemaic system

(Encyclopedia)Ptolemaic system tŏlˌəmāˈĭk [key], historically the most influential of the geocentric cosmological theories, i.e., theories that placed the earth motionless at the center of the universe with a...