SOLAR RADIATION

electromagnetic energy, including X rays, ultraviolet and infrared radiation, and radio emissions, as well as visible light, emanating from the Sun. Of the 3.8 1033 ergs (3.8 1023 kilowatts) emitted by the Sun every second, about 1 part in 120,000,000 is received by its attendant planets and their satellites. The small part of this energy intercepted by the Earth (on the average 1.4 kilowatt per square metre) is of enormous importance to life and to the maintenance of natural processes on the Earth's surface (see also sunlight). The energy output of the Sun has its peak at a wavelength of 0.47 micrometre, and the Sun radiates about eight kilowatts per square centimetre of its surface.