alt=A physical approximation of a black body radiator model constitutes of a heated pyrographite chamber and peripheral devices which ensure temperature stability.|thumb|A black body radiator used in CARLO laboratory in Poland. It is an approximation of a model described by [[Planck's law utilized as a spectral irradiance standard.]]
thumb|upright=1.4|As the temperature of a black body decreases, its radiation intensity also decreases and its peak moves to longer wavelengths. Shown for comparison is the classical [[Rayleigh–Jeans law and its ultraviolet catastrophe.]]
A black body or blackbody is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. The radiation emitted by a black body in thermal equilibrium with its environment is called black-body radiation. The name "black body" is given because it absorbs all colors of light. In contrast, a white body is one with a "rough surface that reflects all incident rays completely and uniformly in all directions."
A black body in thermal equilibrium (that is, at a constant temperature) emits electromagnetic black-body radiation. The radiation is emitted according to Planck's law, meaning that it has a spectrum that is determined by the temperature alone (see figure at right), not by the body's shape or composition.
An ideal black body in thermal equilibrium has two main properties:The idea of a black body originally was introduced by Gustav Kirchhoff in 1860 as follows: