"Version: 20190102"--Title page verso."A Morgan & Claypool publication as part of IOP Concise Physics"--Title page verso.Includes bibliographical references.1. Introduction -- 2. Radiation and atoms -- 2.1. Width and shape of spectral lines -- 2.2. Atomic orders of magnitude -- 2.3. The central field approximation -- 2.4. The form of the central field -- 2.5. Finding the central field3. The cen…