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solar constant

noun
1.
the average rate at which radiant energy is received from the sun by the earth, equal to 1.94 small calories per minute per square centimeter of area perpendicular to the sun's rays, measured at a point outside the earth's atmosphere when the earth is at its mean distance from the sun.
Origin
1865-1870
1865-70
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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British Dictionary definitions for solar-constant

solar constant

noun
1.
the rate at which the sun's energy is received per unit area at the top of the earth's atmosphere when the sun is at its mean distance from the earth and atmospheric absorption has been corrected for. Its value is 1367 watts per square metre
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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solar-constant in Science
solar constant  
The average amount of solar radiation received by the Earth's atmosphere, per unit area, when the Earth is at its mean distance from the Sun. It is equal to 1370 watts per square meter. Solar radiation varies with the Earth's distance from the Sun and with the appearance or decay of sunspots.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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Encyclopedia Article for solar-constant

solar constant

the total radiation energy received from the Sun per unit of time per unit of area on a theoretical surface perpendicular to the Sun's rays and at Earth's mean distance from the Sun. It is most accurately measured from satellites where atmospheric effects are absent. The value of the constant is approximately 1.4 kilowatts per square metre. The "constant" is fairly constant, increasing by only 0.2 percent at the peak of each 11-year solar cycle. Sunspots block out the light and reduce the emission by a few tenths of a percent, but bright spots, called plages, that are associated with solar activity are more extensive and longer lived, so their brightness compensates for the darkness of the sunspots. Moreover, as the Sun burns up its hydrogen, the solar constant increases by about 10 percent every billion years.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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