An equation of radiative transfer (or radiative transfer equation or RTE or transfer equation) is an equation that describes radiative transfer, the transfer of energy by EMR through a gas or plasma, taking into account the absorption and emission of photons by the gas particles. One form:
1 ∂ ^ — ——Iν + Ω˙∇Iν + (kν,s + kν,a)Iν = jν + 1/(4π) kν,s ∫IνdΩ c ∂t
Such equations are often used with approximating assumptions: equilibrium (no change over time), an approximation of the composite of all wavelengths (gray atmosphere, using the Rosseland mean opacity), a directional component (Eddington approximation) and/or that variation in the medium is in a single direction (plane-parallel atmosphere). These are used in models of stellar structure.