How the Saha Ionization Equation Was Discovered

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.