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actinometer
(Encyclopedia)actinometer ăkˌtənŏmˈətər [key], instrument used to measure the heating power of radiation. Actinometers are used chiefly in meteorology to measure solar radiation as transmitted directly by th...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. ...flare, solar
(Encyclopedia)flare, solar: see chromosphere.MacCready, Paul Beattie
(Encyclopedia)MacCready, Paul Beattie, 1925–2007, American engineer and inventor known for his achievements in human-powered flight, b. New Haven, Conn., Ph.D. California Institute of Technology, 1952. In 1997 he...Janssen, Pierre Jules César
(Encyclopedia)Janssen, Pierre Jules César pyĕr zhül sāzärˈ zhäNsĕnˈ [key], 1824–1907, French astronomer. In 1857–58, in Peru, he worked on the determination of the magnetic equator; in the Azores (1867...sun, in astronomy
(Encyclopedia) CE5 Structure of the sun sun, intensely hot, self-luminous body of gases at the center of the solar system. Its gravitational attraction maintains the planets, comets, and other bodies of the sola...Langley, Samuel Pierpont
(Encyclopedia)Langley, Samuel Pierpont, 1834–1906, American scientist, b. Roxbury, Mass., received only a high school education but continued his studies in science in Boston libraries. He became, in 1866, profes...Julian Day calendar
(Encyclopedia)Julian Day calendar, system of astronomical dating that allows the difference between two dates to be calculated more easily than conventional civil calendars with their uneven months. It was devised ...sundial
(Encyclopedia)sundial, instrument that indicates the time of day by the shadow, cast on a surface marked to show hours or fractions of hours, of an object on which the sun's rays fall. Although any object whose sha...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...Browse by Subject
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