The combined effect of the scattering of [electromagnetic radiation](https://learn2.open.ac.uk/mod/glossary/showentry.php?eid=1147003&displayformat=dictionary "S284 Glossary: electromagnetic radiation") by a medium, and [absorption](https://learn2.open.ac.uk/mod/glossary/showentry.php?eid=1147140&displayformat=dictionary "S284 Glossary: absorption") of such radiation by the medium. [[../Chapters/Part 2 Photometry measuring brightness]] [[Docent/S284 Astronomy]]