ABSTRACT
In this chapter, the authors review the basic properties of electromagnetic (EM) radiation that are pivotal to their understanding of the radiation detected from astronomical sources and the design of instrumentation to characterise it. They begin with the wave picture, which can be derived from Maxwell’s equations for the electric and magnetic fields. A transverse travelling wave involves oscillation in a direction perpendicular to the direction of propagation; EM waves are transverse waves. The electric field of the wave causes the particle to oscillate, which, in turn, generates a scattered EM wave with the same frequency, but there is no overall energy exchange between the radiation and the particle. The authors introduce the terminology and method used to quantify the radiation and how it may change as it propagates through a physical medium. An arbitrary wave can be considered as the combination of a linear wave and an elliptically polarised wave.
