The total electromagnetic radiation emitted by the sun. To a first approximation, the sun radiates as a blackbody at a temperature of about 5700 K; hence, about 99. 9% of its energy output falls within the wavelength interval from 0. 15 to 4. 0 μm, with peak intensity near 0. 5 μm. About one-half of the total energy in the solar beam is contained within the visible spectrum from 0. 4 to 0. 7 μm, and most of the other half lies in the near-infrared, a small additional portion lying in the ultraviolet. See insolation, direct solar radiation, diffuse sky radiation, global radiation, extraterrestrial radiation, solar constant, total solar irradiance.