Meghnad Saha was an Indian astrophysicist who created the Saha ionisation equation, which is used to relate the spectral classes of stars to their actual temperatures. His equation works by expressing the relationship between the state of ionization of any particular element in a star and varying temperatures and pressure.
The Saha equation is
where Ni + 1 and Ni are the number of atoms in the (i + 1)th and ith ionization states, respectively; Ui + 1 and Ui describe how energy is partitioned among the (i + 1)th and ith ionization states; Ei + 1 and Ei are the energies of the ionization states; Ne is the number of electrons; and T is the temperature. The other quantities in the equation are physical constants: me is the mass of the electron, k is the Boltzmann constant, and h is Planck’s constant.
– From Britannica, https://www.britannica.com/science/Saha-equation, 23/03/2025
He also built India’s first cyclotron, a particle accelerator that uses a strong magnetic field to propel particles into acceleration in a circular path, and later founded the Saha Institute of Nuclear Physics in Kolkata.
Despite his revolutionary contributions, Saha faced discrimination due to his caste. In the journal he founded, Science and Culture, he wrote about the importance of equality: “To get real freedom, to get rid of illiteracy, to get rid of diseases, ailments, and diseases, we must forget social, political and religious differences.”
Read more about his work in “Meghnad Saha, India’s first cyclotron and the institute of nuclear physics: From the records of the University of Calcutta” by Gautam Gangopadhyay (2025).