Thermal radiation

Summary

Thermal radiation is the electromagnetic radiation that matter emits because of its temperature. It is the only mode of heat transfer that needs no medium, which is how the Sun heats the Earth across empty space. Its upper limit at each wavelength is the radiation of a black body at the same temperature, given by Planck's law. The emitted power grows like the fourth power of the absolute temperature, so radiation dominates heat transfer at high temperatures.