  Although the Saha ionization equation is a standard topic in advanced
statistical physics and most professional physicists would have some knowledge
of it, the exact nature of Meghnad Saha's contributions in this subject is not
widely known. Based on an analysis of Saha's original papers and other relevant
papers by contemporary scientists, as well as other source materials such as
letters exchanged between scientists, I discuss how Saha used the theory of
thermal ionization to solve some of the most important astrophysics problems of
that era.
