Essential Radio Astronomy by James J. Condon and Scott M. Ransom Created 2026-10-20 Updated 2026-11-05
Official course and author record: science.nrao.edu/opportunities/courses/era
NRAO-hosted authored text. Equations (4.57)–(4.60) define emission measure, radio optical depth and optically thick/thin observables. The course page identifies both authors and the 12 March 2016 preface date.