Meghnad Saha

Meghnad Saha (6 October 1893 – 16 February 1956) was an Indian astrophysicist and politician who helped devise the theory of thermal ionisation. His Saha ionisation equation allowed astronomers to accurately relate the spectral classes of stars to their actual temperatures.

Meghnad Saha was born on 6 October 1893 to a lower caste Bengali Hindu family in the village of Sheoratali in Gazipur, then part of the Dacca district of the Bengal Presidency (now Bangladesh). He was the fifth of eight children born to Jagannath Saha, a poor shopkeeper, and his wife, Bhubaneshwari Devi. Due to the superstitious religious ideologies of the orthodox, haughty Brahmins of the time and his childhood and career experiences of casteism, being a Namasudra (classified as Dalits), Saha developed a hatred for the caste system from a young age.

During his youth, he was forced to leave Dhaka Collegiate School because he participated in the Swadeshi movement. After that, he joined K. L. Jubilee High School & College. He earned his Indian School Certificate from Dhaka College. He was also a student at the Presidency College, Kolkata, and Rajabazar Science College CU. Saha faced discrimination from other students due to his caste; when he was at the Eden Hindu Hostel, communal students objected to him eating in the same dining hall as them.

He 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 a Fellow of the Royal Society in 1927. He was president of the 21st session of the Indian Science Congress in 1934.

Amongst Saha's classmates were Satyendra Nath Bose, Jnan Ghosh, and Jnanendra Nath Mukherjee. In his later life, he was close to Amiya Charan Banerjee.

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:

It will be admitted from what has gone before that the temperature plays the leading role in determining the nature of the stellar spectrum. Too much importance must not be attached to the figures given, for the theory is only a first attempt for quantitatively estimating the physical processes taking place at high temperature. We have practically no laboratory data to guide us, but the stellar spectra may be regarded as unfolding to us, in an unbroken sequence, the physical processes succeeding each other as the temperature is continually varied from 3000 K to 40,000 K.

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