Astronomy is perhaps the most ancient of all sciences, but astrophysics had its origins only in the twentieth century. One of the pioneers in this field was Meghnad Saha (born: 6 October 1894) who was also an influential scientific leader of twentieth century India.
Saha obtained a teaching position in Mathematics at Calcutta University. Here, he came into conflict with the department head. So he moved to the department of physics: a subject which he had studied only up to the undergraduate level. So he plunged into the materials and mastered them as he carried through his teaching assignments.
Meghnad Saha’s interests were drawn to astrophysics. To learn the subject he began a systematic study of twenty-five years of the Monthly Notices of the Royal Astronomical Society. He did some experimental work also in the meanwhile, such as devising methods for measuring light pressure. Many of his results, both theoretical and experimental, were published in international journals of physics. By 1918 he had done sufficient work to receive a doctor’s degree. He was only twenty-four.
While teaching thermodynamics, Saha thought of applying it and quantum theory to stellar matter. In chemistry one talks of chemical dissociation: the breakdown of molecules into atoms at high temperatures. In atomic physics one speaks of ionization: the stripping of electrons from atoms, usually at high voltages or temperatures. Saha drew an analogy between the two, and derived a formula by which the degree of ionization in a very hot gas could be expressed in terms of its temperature and electron pressure.
This is very relevant in the study of the solar spectra and the stars, a topic that is of the utmost importance in understanding the nature and composition of those distant bodies. Saha’s very important results on this subject were published in a classic paper entitled, “On Ionization in the Solar Chromosphere,” in the prestigious Philosophical Magazine in 1920. The problems considered in this paper are of enormous moment: they had been suggested by Niels Bohr to some of the brightest physicists of the time.
Astronomers had long been puzzled by the absence of certain spectra in the sun. It followed from Saha’s analysis that on the basis of the temperature and the ionization potentials of these elements, they would not be present in the very hot regions. Saha’s theory of stellar spectra was the starting point of modern astrophysics.
In the meanwhile, as other physicists extended and confirmed his theory, Saha’s international reputation grew. He received many professional honors. In 1925 he was elected president of the physics section of the Indian Science Congress Association. In 1927 he was elected Fellow of the Royal Society. Saha was instrumental in establishing the National Academy of Sciences. He also founded the influential socio-scientific journal, Science and Culture, which continues with full vigor.
During India’s freedom struggle, Saha devoted his intellectual energies to science and its development in India. Saha was not very enthusiastic about the khadi movement by which Gandhi and his followers encouraged cottage industries for spinning and weaving. Saha feared this would impede India’s industrial development.
After Indian independence Saha spent much of his time and energy for solving the social, economic and political problems facing the country. He tried to rid his people of superstitions and astrology, though not very successfully. He was elected to Parliament. It was good that not all the brilliant minds of the country were expended in that urgent and time consuming call for freedom from the British. Scientists are as important for any developing country as politicians, the military and business leaders.
October 6, 2013