Reradiation
Reradiation is the emission of electromagnetic radiation by a material after it has absorbed energy from another source. It is a form of radiative relaxation and can occur through several mechanisms, including thermal emission, fluorescence, and phosphorescence. In thermal reradiation, absorbed energy raises the object's temperature, and the object emits a spectrum described by blackbody or graybody radiation, governed by its temperature and emissivity. In fluorescence and phosphorescence, energy is temporarily stored in excited electronic states and released as photons, typically at characteristic wavelengths, with fluorescence occurring rapidly and phosphorescence on longer timescales.
The spectral distribution of reradiated light depends on the mechanism and material properties. Thermal reradiation follows
In planetary and astrophysical contexts, reradiation strongly influences energy balance. Dust and gas that absorb stellar
Kirchhoff's law relates reradiation to absorption: for a body in thermal equilibrium, emissivity at a given
Applications of studying reradiation include infrared astronomy, climate modeling, and materials characterization, where emissivity, radiance, and