October 6: Meghnad Saha

Meghnad Saha

October 6, 1893 – February 16, 1956

Meghnad Saha was an Indian astrophysicist best known for his development of the Saha equation, used to describe chemical and physical conditions in stars.

Saha was a professor at Allahabad University from 1923 to 1938, and thereafter a professor and Dean of the Faculty of Science at the University of Calcutta until his death in 1956. He became Fellow of the Royal Society in 1927. He was president of the 21st session of the Indian Science Congress in 1934.

Saha was fortunate to have brilliant teachers and class fellows. In his student days, Jagadish Chandra Bose and Prafulla Chandra Roy were at the pinnacle of their fame. Amongst his class fellows were Satyendra Nath Bose, Jnan Ghosh and J. N. Mukherjee. In later life he was close to Amiya Charan Banerjee, a renowned mathematician at Allahabad University.

Meghnad Saha's best-known work concerned the thermal ionisation of elements, and it led him to formulate what is known as the Saha equation. This equation is one of the basic tools for interpretation of the spectra of stars in astrophysics. By studying the spectra of various stars, one can find their temperature and from that, using Saha's equation, determine the ionisation state of the various elements making up the star.

Saha also helped to build several scientific institutions, such as the Physics Department in Allahabad University and the Institute of Nuclear Physics in Calcutta. He founded the journal Science and Culture and was the editor until his death. He was the leading spirit in organizing several scientific societies, such as the National Academy of Science (1930), the Indian Physical Society (1934), Indian Institute of Science (1935) and the Indian Association for the Cultivation of Science (1944). A lasting memorial to him is the Saha Institute of Nuclear Physics, founded in 1943 in Kolkata.

He also invented an instrument to measure the weight and pressure of solar rays.

"The impetus given to astrophysics by Saha’s work can scarcely be overestimated, as nearly all later progress in this field has been influenced by it and much of the subsequent work has the character of refinements of Saha’s ideas." - S. Rosseland

The Lunar crater Saha is named in his honor.