I gave this course RTSA yearly during 1994 - 2007 to masters students (132 in total) at the former Sterrekundig Instituut of Utrecht University. The main topic is the classical theory of radiative transfer for explaining stellar spectra. It needs relatively much attention to be mastered. Radiative transfer in gaseous media that are neither optically thin nor fully opaque and scatter to boot is a key part of astrophysics but not a transparent subject. These course notes represent a middle road between Mihalas' Stellar Atmospheres (graduate level and up) and the books by Novotny and Boehm-Vitense (undergraduate level). They are at about the level of Gray's The observation and analysis of stellar photospheres but emphasize NLTE radiative transfer rather than observational techniques and data interpretation.
The printing of these course notes may take hours because they unpack to about 160 Mbyte PostScript, due to many scanned graphs. If you share a printer with others you might print them overnight, or in parts using the “from-to” button in your pdf reader print menu. A black & white printer suffices.
The accompanying equation compendium displays all numbered equations in the course notes, identically and with the same numbers, grouped per topic and in large font for projection (in portrait format for 1990s-style overhead transparencies). You have to skip the first pages.
The second chapter is a summary of my introductory course for bachelor students Introduction to Astrophysical Radiative Transfer. Part of that course I also summarized for NSO summer students in 1993 as Introduction to Solar Spectrum Formation.
Teachers and self-studiers may request my answers to many problems in the last section.
Erratum (not the only one): below (3.66) on page 59.
An update including filling many missing paragraphs remains on my long-term to-do list since 2003. However, in 2021 I wrote Compendium solar spectrum formation (arXiv, ADS) summarized on this page. It is a brief-looking but comprehensive webbased course which links directly to many RTSA pages for basic radiative transfer theory while also linking to many didactic displays made in the meantime. It then adds newer developments, in particular non-equilibrium analysis and chromospheric spectrum formation, and treats many specific line formation issues and related solar physics topics in detailed optional endnotes, with many direct page openers of ADS-public literature.