ABSTRACT
This chapter deals with the transfer of radiation in a dusty medium. It summarizes the elements of radiative transfer, discusses the general transfer equation and sketches how to derive, for a homogeneous medium, estimates on temperature, density and masses. The chapter presents a set of equations for spherical dust clouds that treats radiative cooling and heating in an energetically consistent way and outline how to solve it numerically. The dust emission of a cloud is observed at various wavelengths with the goal of deriving its internal structure. The observational data consist either of maps or of single point measurements towards different positions on the source obtained with different spatial resolution. In practice, however, one may encounter difficulties using a public code because it usually has to be modified to meet the demands of a specific astronomical problem. The chapter presents the equations and sketch the numerical strategy for such an endeavour in spherical symmetry.
