The Planck law gives the intensity radiated by a blackbody as a function of frequency (or wavelength). Let a blackbody have temperature T. Let be the energy density per unit solid angle so that

(1)

then the blackbody radiates at a frequency with spectral energy density

(2)

where h is Planck's constant, c is the speed of light, and k is Boltzmann's constant (Rybicki and Lightman 1979, p. 21).

Blackbody, Blackbody Radiation, Brightness Temperature, Planck Intensity Density, Rayleigh-Jeans Spectrum, Stefan-Boltzmann Law, Thermal Radiation, Wien's Displacement Law, Wien Law