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Tropic of Cancer

(Encyclopedia)Tropic of Cancer, parallel of latitude at 23°30′ north of the equator; it is the northern boundary of the tropics. This parallel marks the farthest point north at which the sun can be seen directly...

rammed earth

(Encyclopedia)rammed earth, material consisting chiefly of soil of sufficiently stiff consistency that has been placed in forms and pounded down. It has been used for buildings and walls since ancient times and was...

solar constant

(Encyclopedia)solar constant, the average amount of radiant energy received by the earth's atmosphere from the sun; its value is about 2 calories per min incident on each square centimeter of the upper atmosphere. ...

Hu Han-min

(Encyclopedia)Hu Han-min ho͞o hän-mĭn [key], 1879–1936, Chinese statesman. While studying law in Japan (1905) he was associated with Sun Yat-sen in revolutionary activities. After the revolution of 1911, Hu op...

corona, in astronomy

(Encyclopedia)corona, luminous envelope surrounding the sun, outside the chromosphere. Its density is less than one billionth that of the earth's atmosphere. The corona is visible only at the time of totality durin...

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...

rainbow

(Encyclopedia)rainbow, arc showing the colors of the spectrum, violet inside and red outside, which appears when the sun shines through water droplets. It often appears while the sun is shining after a brief thunde...

coronagraph

(Encyclopedia)coronagraph kərōˈnəgrăfˌ [key], device invented by the French astronomer B. Lyot (1931) for the purpose of observing the corona of the sun and solar prominences occurring in the chromosphere. Be...

photosphere

(Encyclopedia)photosphere, luminous, apparently opaque layer of gases that forms the visible surface of the sun or any other star. The photosphere lies between the dense interior gases and the more attenuated gases...

Fraunhofer lines

(Encyclopedia)Fraunhofer lines frounˈhôfər [key]: see sun. ...