ABSTRACT
This chapter explains the physical background of dust emission. A single grain radiates according to Kirchhoff’s law and the law is derived under the assumption that a grain consists of an ensemble of coupled harmonic oscillators in thermal equilibrium. The chapter shows how to compute the temperature to which a grain is heated in a radiation field and add a few common examples as well as useful approximation formulae. It illustrates the emission of grains for a typical dust type; it also presents a first example of radiative transfer, for a dust cloud of uniform temperature. The chapter investigates the calorific properties of dust and presents examples of the emission of very small grains. A grain bathed in a radiation field acquires an equilibrium temperature which is determined by the condition that it absorbs per second as much energy as it emits.
