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physical fitness

(Encyclopedia)physical fitness, combined good health and physical development. The object of any program of physical fitness is to maximize an individual's health, strength, endurance, and skill relative to age, se...

zodiacal light

(Encyclopedia)zodiacal light or zodiacal band, a faint band of light sometimes seen in the western sky just after sunset in the spring, extending up from the horizon at the point where the sun has just set, or in t...

Galileo

(Encyclopedia)Galileo (Galileo Galilei) gălˌĭlēˈō; gälēlĕˈō gälēlĕˈē [key], 1564–1642, great Italian astronomer, mathematician, and physicist. By his persistent investigation of natural laws he la...

glacial periods

(Encyclopedia)glacial periods, times during which large portions of the earth's surface were covered with thick glacial ice sheets. In the Pleistocene epoch, in the Carboniferous and Permian periods of the Paleozoi...

Aristarchus of Samos

(Encyclopedia)Aristarchus of Samos ărˌĭstärˈkəs, sāˈmŏs [key], fl. c.310 b.c.–c.230 b.c., Greek astronomer and mathematician of the Alexandrian school. He is said to have been the first to propose a heli...

Eddington, Sir Arthur Stanley

(Encyclopedia)Eddington, Sir Arthur Stanley, 1882–1944, British astronomer and physicist. He was chief assistant (1906–13) at the Royal Observatory, Greenwich, and was from 1913 Plumian professor of astronomy a...

Stegosaurus

(Encyclopedia)Stegosaurus stĕgəsôrˈəs [key] [Gr.,=roof lizard], quadriped ornithischian dinosaur of the late Jurassic period. About 29 ft 6 in (9 m) long, it had short forelegs, four long bony spikes on a flex...

navigation satellite

(Encyclopedia)navigation satellite, artificial satellite designed expressly to aid the navigation of sea and air traffic. Early navigation satellites, from the Transit series launched in 1960 to the U.S. navy's Nav...

Tesla, Nikola

(Encyclopedia)Tesla, Nikola tĕsˈlə [key], 1856–1943, American electrician and inventor, b. Croatia (then an Austrian province). An ethnic Serb, he immigrated to the United States in 1884, worked for a short pe...

distortion

(Encyclopedia)distortion, in electronics, undesired change in an electric signal waveform as it passes from the input to the output of some system or device. In an audio system, distortion results in poor reproduct...