Blackbody Radiation: Physical Mechanisms

A blackbody spectrum has a smooth distribution with a temperature-dependent peak. Wien's law links temperature to the wavelength of maximum emission, while the Stefan-Boltzmann law says emitted power per unit area grows as the fourth power of absolute temperature.

Thermal motion in matter produces a distribution of electromagnetic emission. Raising temperature increases the total emitted energy and shifts the peak toward shorter wavelengths because higher-energy modes become more strongly populated.

Laboratory cavities approximate blackbodies, and stellar spectra show temperature-dependent continuum shapes. The Sun's photospheric continuum corresponds roughly to a temperature near 5800 K even though absorption lines are superimposed.

Blackbody radiation emerges from matter and radiation approaching thermal equilibrium. Classical physics failed at short wavelengths, producing the ultraviolet catastrophe; Planck's quantized energy assumption supplied the correct spectrum and helped launch quantum theory. In stars, photons interact repeatedly in optically thick layers before escaping from a photosphere, which is why a thermal-like continuum can form even though individual microscopic emission processes are complicated.