说明：  A black body is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence.Black-body radiation is distributed in energy (or frequency) in a manner set by the temperature T. A black body in thermal equilibrium emits electromagnetic radiation called 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. Practical materials emit energy at a fraction of black-body energy levels called the emissivity of the surface. By definition, a black body in thermal equilibrium has an emissivity of ε = 1.0. A source with lower emissivity independent of frequency often is referred to as a gray body. Construction of black bodies with emissivity as close to one as possible remains a topic of current interest. This code can be used to simulate the black body radiation.