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Van Allen radiation belts

(Encyclopedia)CE5 Van Allen radiation belts: The solar wind, a stream of protons, electrons, and ions coming from the sun, gives the belts their asymmetrical shape. Van Allen radiation belts, belts of radiation...

Ptolemy

(Encyclopedia)Ptolemy (Claudius Ptolemaeus), fl. 2d cent. a.d., celebrated Greco-Egyptian mathematician, astronomer, and geographer. He made his observations in Alexandria and was the last great astronomer of ancie...

radiation

(Encyclopedia)radiation rāˌdēāˈshən [key], term applied to the emission and transmission of energy through space or through a material medium and also to the radiated energy itself. In its widest sense the te...

Pachacamac

(Encyclopedia)Pachacamac päˌchäkämäkˈ [key], ruins of a walled Native American settlement, Peru, about 25 mi (40 km) SE of Lima in the Lurin Valley. This site, which contains a number of pyramids, was conside...

pigeon

(Encyclopedia)pigeon, common name for members of the large family Columbidae, land birds, cosmopolitan in temperate and tropical regions, characterized by stout bodies, short necks, small heads, and thick, heavy pl...

wild rice

(Encyclopedia)wild rice, tall aquatic plant (Zizania aquatica) of the family Poaceae (grass family), of a genus separate from common rice (Oryza). Wild rice (called also Canada rice, Indian rice, and water oats) is...

zodiac

(Encyclopedia)CE5 Signs of the zodiac CEE zodiac zōˈdēăk [key] [Gr. zoion=animal], in astronomy, zone of the sky that includes about 8° on either side of the ecliptic. The apparent paths of the sun, the...

centripetal force and centrifugal force

(Encyclopedia)CE5 Centripetal and centrifugal forces: When a ball is swung in a circle at the end of a string, centripetal and centrifugal forces act as shown above. centripetal force and centrifugal force, act...

Plato

(Encyclopedia)Plato plāˈtō [key], 427?–347 b.c., Greek philosopher. Plato's teachings have been among the most influential in the history of Western civilization. Many of the late dialogues are devoted to te...

Inca

(Encyclopedia)Inca ĭngˈkə [key], pre-Columbian empire, W South America. The name Inca may specifically refer to the emperor, but is generally used to mean the empire or the people. When Francisco Pizarro lande...