Black-body radiation

In physics, a black body is an idealized body which absorbs all radiation and emits radiation in a spectrum determined by its temperature. Planets and stars (including the earth and sun) can be approximated as black bodies. The intensity of radiation emitted by the black body $I=\langle|\mathbf S|\rangle$ is related to its temperature $T$ by the equation:

Where $\epsilon \in [0,1]$ is the emissivity and $\sigma$ is the Stefan-Boltzmann constant. An ideal black body has emissivity $\epsilon=1$.

The wavelength emitted varies with the temperature as well. The graph below shows the wavelength and intensity of radiation emitted by a black body at different temperatures.