Radiation

The third way to transfer heat, in addition to convection and conduction, is by radiation, where energy is transferred in the form of electromagnetic waves. An electromagnetic wave is basically an oscillating electric and magnetic field traveling through space at the speed of light. All of us are already familiar with many kinds of electromagnetic waves, such as radio waves, microwaves, the light we see, X-rays, and ultraviolet rays. The only difference between the different kinds is the frequency and wavelength of the wave.

The radiation here, in regard to heat transfer, is not the same thing as the dangerous radiation associated with nuclear bombs. That radiation comes in the form of very high energy electromagnetic waves, as well as nuclear particles. The radiation associated with heat transfer is entirely electromagnetic waves, with a relatively low (and hence relatively safe) energy.
Everything around us takes in energy from radiation, and gives it off in the form of radiation. When everything is at the same temperature, the amount of energy received is equal to the amount given off. Because there is no net change in energy, no temperature changes occur. When things are at different temperatures, however, the hotter objects give off more energy in the form of radiation than they take in; the reverse is true for the colder objects.