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Eratosthenes

(Encyclopedia)Eratosthenes ĕrətŏsˈthənēz [key], c.275–c.195 b.c., Greek scholar, b. Cyrene. A pupil of Callimachus in Athens, he became (c.240 b.c.) head of the library at Alexandria. Known for his versatil...

Painlevé, Paul

(Encyclopedia)Painlevé, Paul pōl păNləvāˈ [key], 1863–1933, French statesman and mathematician. A mathematical prodigy when a child, he entered on a career devoted to science. He was a professor at the Sorb...

Ritchey, George Willis

(Encyclopedia)Ritchey, George Willis, 1864–1945, American astronomer, b. Meigs co., Ohio, studied at the Univ. of Cincinnati (1883–84, 1886–87). He was superintendent of instrument construction (1899–1904) ...

Biot, Jean Baptiste

(Encyclopedia)Biot, Jean Baptiste zhäN bätēstˈ byō [key], 1774–1862, French physicist, grad. École Polytechnique (1797). He taught mathematics at Beauvais before becoming (1800) professor of mathematical ph...

zenith

(Encyclopedia)zenith, in astronomy, the point in the sky directly overhead; more precisely, it is the point at which the celestial sphere is intersected by an upward extension of a plumb line from the observer's lo...

proper motion

(Encyclopedia)proper motion, in astronomy, apparent movement of a star on the celestial sphere, usually measured as seconds of arc per year; it is due both to the actual relative motions of the sun and the star thr...

Dyson, Sir Frank Watson

(Encyclopedia)Dyson, Sir Frank Watson dīˈsən [key], 1868–1939, English astronomer, b. Ashby-de-la-Zouch, grad. Cambridge. He was astronomer royal of Scotland (1905–10) and of England (from 1910). As director...

Al-Biruni, Abu Rayhan Muhammad ibn Ahmad

(Encyclopedia)Al-Biruni or Al Beruni, Abu Rayhan Muhammad ibn Ahmad äbo͞oˈ rīhänˈ məhămˈĭd ĭbˈən äˈməd ăl-bēro͞oˈnē, ăl bĕro͞oˈnē [key], b. 973, d. after 1050, Central Asian scientist. His...

color index

(Encyclopedia)color index, in astronomy, difference in an object's brightness as recorded between any two well-defined bands of the electromagnetic spectrum by using optical filters of different colors. If blue and...

Chaldaea

(Encyclopedia)Chaldaea or Chaldea both: kăldēˈə [key], properly the southernmost portion of the valley of the Tigris and the Euphrates rivers. Sometimes it is extended to include Babylonia and thus comprises al...