Saha, Meghnad (māgnädˈ säˈhä) [key], 1893–1956, Indian physicist. He was a professor at Allahabad Univ. from 1923 to 1938 and a professor and physics department head at Calcutta Univ. from 1938. His theory of high-temperature ionization of elements and its application to stellar atmospheres, expressed in the Saha equation, is fundamental to modern astrophysics; subsequent development of his ideas has led to increased knowledge of the pressure and temperature distributions of stellar atmospheres.