Question: What equation is this Indian astrophysicist who founded Indian Physical Society best known for?
Context: Deb Shankar Ray (born 1954) is an Indian physical chemist and professor at the department of physical chemistry of the Indian Association for the Cultivation of Science, Kolkata.  He is known for his researches on non-linear dynamics and theoretical spectroscopy and is an elected fellow of the Indian National Science Academy West Bengal Academy of Science and Technology and the Indian Academy of Sciences The Council of Scientific and Industrial Research, the apex agency of the Government of India for scientific research, awarded him the Shanti Swarup Bhatnagar Prize for Science and Technology, one of the highest Indian science awards, in 1999, for his contributions to chemical sciences. Mahendra Kumar Verma is an Indian physicist and professor at the Indian Institute of Technology Kanpur, working on fluid dynamics, turbulence, and nonlinear dynamics.  Verma earned his bachelor's degree in computer science from the Indian Institute of Technology Madras in 1988, and a Ph.D. in physics from the University of Maryland, College Park in 1994.  He is a member of the Indian Physical Society and was awarded the Swarnajayanti Fellowship by the Department of Science and Technology, Government of India in 2006. Meghnad Saha FRS (6 October 1893 – 16 February 1956) was an Indian astrophysicist best known for his development of the Saha ionization equation, used to describe chemical and physical conditions in stars.  Saha was the first scientist to relate a star's spectrum to its temperature, developing thermal ionization equations that have been foundational in the fields of astrophysics and astrochemistry.  He was repeatedly and unsuccessfully nominated for the Nobel Prize in Physics.  Saha was also politically active and was elected in 1952 to India's parliament. Mulugeta Bekele (born 1947) is an Ethiopian scientist and academic.  He is an associate Professor Physics at Addis Ababa University (AAU), Ethiopia.  He completed his PhD in Physics at the Indian Institute of Science, Bangalore, India in 1997.  He has been awarded the Andrei Sakharov Prize by the American Physical Society (APS) "For tireless efforts in defense of human rights and freedom of expression and education anywhere in the world, and for inspiring students, colleagues and others to do the same."  He is the president of Ethiopian Physical Society since October 1998 and an Associate Member of the Abdus Salam International Centre for Theoretical Physics, Trieste, Italy since May 1999. The Saha ionization equation, also known as the Saha–Langmuir equation, is an expression that relates the ionization state of an element to the temperature and pressure.  The equation is a result of combining ideas of quantum mechanics and statistical mechanics and is used to explain the spectral classification of stars.  The expression was developed by the Indian astrophysicist Meghnad Saha in 1920, and later (1923) by Irving Langmuir. James Lattimer is a nuclear astrophysicist who works on the dense nuclear matter equation of state and neutron stars.  He is a Distinguished Professor of Physics and Astronomy at Stony Brook University.  He is an American Physical Society Fellow (2001), Sadhan Basu (1922–1992) was an Indian physical chemist, academic and the Palit Professor of Chemistry at the University of Calcutta.  He was known for his elucidation of the Quantum Mechanical Model of Robert S. Mulliken and his article, "Degree of Polymerization and Chain Transfer in Methyl Methacrylate", co-authored by Jyotirindra Nath Sen and Santi R. Palit was the first published Indian article on polymer chemistry.  He was an elected fellow of the Royal Society of Chemistry, Chemical Society of France, Indian Chemical Society, Indian National Science Academy and the Indian Academy of Sciences.  The Council of Scientific and Industrial Research, the apex agency of the Government of India for scientific research, awarded him the Shanti Swarup Bhatnagar Prize for Science and Technology, one of the highest Indian science awards, in 1962, for his contributions to chemical sciences. The Indian Physical Society is a professional society of physicists in India.  It was formally established in 1934 by pioneering Indian physicist Meghnad Saha.  The society's stated objectives are to promote the progress and uphold the cause of both pure and applied physics in India, to encourage publications in physics and related areas, to publisher books, journals, proceedings etc., to organize conferences, advise government bodies, and to secure and administer funds, grants and endowments for the furtherance of scientific research. Vijay Kumar Kapahi (21 January 1944 – 16 March 1999) was an Indian astrophysicist and the director of the National Centre for Radio Astrophysics, an autonomous division of Tata Institute of Fundamental Research.  Known for his research on radio galaxies, quasars and observational cosmology, Kapahi was an elected fellow of all the three major Indian science academies – Indian Academy of Sciences, Indian National Science Academy and National Academy of Sciences, India – as well as of the Maharashtra Academy of Sciences.  The Council of Scientific and Industrial Research, the apex agency of the Government of India for scientific research, awarded him the Shanti Swarup Bhatnagar Prize for Science and Technology, one of the highest Indian science awards, for his contributions to physical sciences in 1987. Mihir Chowdhury (born 1937) was an Indian physical chemist and Professor and Head of Department of Physical Chemistry at Presidency College, Kolkata and the Indian Association for the Cultivation of Science (IACS).  He is known for his studies on the electronic structure of molecules using optical, magneto-optical and quantum-mechanical methods.  He was an elected fellow of the Indian National Science Academy and the Indian Academy of Sciences.  The Council of Scientific and Industrial Research, the apex agency of the Government of India for scientific research, awarded him the Shanti Swarup Bhatnagar Prize for Science and Technology, one of the highest Indian science awards, in 1977, for his contributions to chemical sciences.
Answer: Saha ionization equation