Meghnad Saha was an Indian astrophysicist 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. Saha's equation is considered one of the ten most outstanding discoveries in astronomy and astrophysics since Galileo's invention of the telescope in 1608. He was elected as an independent member to the Parliament of India in 1952.

In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the rainbow of colors interspersed with spectral lines. Each line indicates a particular chemical element or molecule, with the line strength indicating the abundance of that element. The strengths of the different spectral lines vary mainly due to the temperature of the photosphere, although in some cases there are true abundance differences. The spectral class of a star is a short code primarily summarizing the ionization state, giving an objective measure of the photosphere's temperature.