Saha's study of the thermal ionisation of elements led him to formulate what is known as the Saha ionisation equation. This equation is one of the basic tools for interpreting the spectra of stars. By studying the spectra of stars, one can find their temperature and using Saha's equation determine the ionisation state of the elements making up the star. This was extended by Ralph H. Fowler and Edward Arthur Milne. Saha had previously reached the following conclusion on the subject: