The
sun unit (abbreviated
SU) is a measure of sun intensity weighted for skin damage related to the
UV indexThe UV index is an international standard measurement of how strong the ultraviolet radiation from the sun is at a particular place on a particular day...
.
Solar radiation sustains life on earth and determines climate. The energy flow within the sun results in a surface temperature of around 5800 K, so the spectrum of the radiation from the sun is similar to that of a 5800 K blackbody with fine structure due to absorption in the cool peripheral solar gas (
Fraunhofer linesIn physics and optics, the Fraunhofer lines are a set of spectral lines named for the German physicist Joseph von Fraunhofer . The lines were originally observed as dark features in the optical spectrum of the Sun....
).
The irradiance of the sun on the outer atmosphere when the sun and earth are spaced at 1 AU—the mean earth/sun distance of 149,597,870 km—is called the solar constant.
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The
sun unit (abbreviated
SU) is a measure of sun intensity weighted for skin damage related to the
UV indexThe UV index is an international standard measurement of how strong the ultraviolet radiation from the sun is at a particular place on a particular day...
.
Basics of solar radiation
Solar radiation sustains life on earth and determines climate. The energy flow within the sun results in a surface temperature of around 5800 K, so the spectrum of the radiation from the sun is similar to that of a 5800 K blackbody with fine structure due to absorption in the cool peripheral solar gas (
Fraunhofer linesIn physics and optics, the Fraunhofer lines are a set of spectral lines named for the German physicist Joseph von Fraunhofer . The lines were originally observed as dark features in the optical spectrum of the Sun....
).
Solar constant and "sun value"
The irradiance of the sun on the outer atmosphere when the sun and earth are spaced at 1 AU—the mean earth/sun distance of 149,597,870 km—is called the solar constant. Currently accepted values are about 1360 W/m² (the NASA value given in ASTM E 490-73a is 1353 ±21 W/m²). The World Metrological Organization (WMO) promotes a value of 1367 W/m².