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continuous curve with a sincle maximum, which occurs at a specific 
wave length for a given temperature. The relationship is given by 
Wien's displacement law, 
(wave length for radiation of maximum intensity) x (absolute 
temperature) = 2900 microns. 
This maximum is at 0.5 micron for solar radiation, at 10 microns for 
em 2déal radiator at 50°F, The micron is a unit of length equivalent 
to a thousandth of a millimeter. For comparison, the visible band 
Of the spectrum is from 0.4 to 0.7 micron. As the temperature in- 
creases, the emission in each wave: “length increases, but the increase 
is more rapid in the shorter wave lengths so the maximum shifts to 
shorter wave lengths. 
The intensity of radiation from a body in space varies as the 
inverse sauare of the distance from the body. Hence the intensity of 
solar radiation at the earth's distance fron the sun is only about 
0.00002 of its intensity at the sun's surface. Since the solar radi- 
ation is reduced to this extremely small fraction its spectral energy 
distribution falls to practically zero except near the pveaks only an 
undetectable amount remains inwave lengths longer than about 3 microns. 
On the other hand the radiation from an ideal radiator at any atmos- 
pherie or oceanic temperature has utterly negligible intensity in 
wave lengths less than 3 microns. Hence the two snectra are mutually 
exclusive, so that solar (short-wave) radiation and terrestrial 
{long-wave) radiation can be treated entirely separately. 
The intensity of the radiation in the solar beam in free space 
at the earth's mean distance from the sun is known in meteorology as 
the solar constant. Its value is about 2800 cal em-2 day-l. 
The albedo of the earth as a whole is about 0.43, which means 
that 43 per cent of the solar radiation intercepted by the earth is 
