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Great Rift Valley

(Encyclopedia)Great Rift Valley, geological fault system of SW Asia and E Africa. It extends c.3,000 mi (4,830 km) from N Syria to central Mozambique. The northernmost extension runs S through Syria and Lebanon, th...

Turner, Frederick Jackson

(Encyclopedia)Turner, Frederick Jackson, 1861–1932, American historian, b. Portage, Wis. He taught at the Univ. of Wisconsin from 1885 to 1910 except for a year spent in graduate study at Johns Hopkins. From 1910...

americium

(Encyclopedia)americium ămərĭˈshēəm [key], artificially produced radioactive chemical element; symbol Am; at. no. 95; mass no. of most stable isotope 243; m.p. about 1,175℃; b.p. about 2,600℃; sp. gr. 13....

Fourier, Charles

(Encyclopedia)Fourier, Charles shärl fo͞oryāˈ [key], 1772–1837, French social philosopher. From a bourgeois family, he condemned existing institutions and evolved a kind of utopian socialism. In Théorie des ...

Hudson River school

(Encyclopedia)Hudson River school, group of American landscape painters, working from 1825 to 1875. The 19th-century romantic movements of England, Germany, and France were introduced to the United States by such w...

Hanover, house of

(Encyclopedia)Hanover, house of, ruling dynasty of Hanover (see Hanover, province), which was descended from the Guelphs and which in 1714 acceded to the British throne in the person of George I. George was the gra...

atomic clock

(Encyclopedia)atomic clock, electric or electronic timekeeping device that is controlled by atomic or molecular oscillations. A timekeeping device must contain or be connected to some apparatus that oscillates at a...

tower

(Encyclopedia)tower, structure, the greatest dimension of which is its height. Towers have belonged to two general types. The first embodies practical uses such as defense (characteristic of the Middle Ages), to ca...

binary star

(Encyclopedia)CE5 A. Eclipsing binary: Primary component passing behind secondary (dimmer) component B. Light curve for eclipsing binary binary star or binary system, pair of stars that are held together by the...

X-ray astronomy

(Encyclopedia)X-ray astronomy, study of celestial objects by means of the X rays they emit, in the wavelength range from 0.01 to 10 nanometers. X-ray astronomy dates to 1949 with the discovery that the sun emits X ...