Radiation
Thermal energy emitted by matter as a result of vibrational and rotational movements of molecules, atoms and electrons. The energy is transported by electromagnetic waves (or photons). Radiation requires no medium for its propagation, therefore, can take place also in vacuum. All matters emit radiation as long as they have a finite (greater than absolute zero) temperature. The rate at which radiation energy is emitted is usually quantified by the modified Stefan-Bolzmann law:
where the emissivity, e , is a property of the surface characterizing how effectively the surface radiates compared to a "blackbody" (0<eə ). E=q/A (W/m2) is the surface emissive power. s is the Stefan-Boltzmann constant
(s=5.67x10-8 W/(m2K4)). Tb is the absolute temperature of the surface (in Kelvin).