125th Birth Anniversary
Meghnad Saha
(1893-1956)

Indian astrophysicist Meghnad Saha was born in a village near Dhaka, then Dacca in east Bengal, and today the capital of Bangladesh. He came from a humble Dalit background, his father Jagannath was a grocer. Apparently he was named Meghnath, but he renamed himself Meghnad, after Ravana's brother from the {Ramayana}, who was portrayed as a hero in the poem "Meghnad badh" by Bangla poet and dramatist Michael Madhusudan Dutt, which impressed him very much.
He had to leave school when caught in the protests of the {swadeshi} movement, which erupted when the province of Bengal was partitioned into two by the British viceroy Lord Curzon in 1905. West Bengal had population with Hindu majority and East Bengal had Muslim majority. Luckily he was a good student, got admission and completed his school exams from Dhaka College. He then studied physics at Presidency College in Calcutta. Most of his work was done while he was at Allahabad University, where he was until 1936. Then he moved to the University of Calcutta.
Saha brought out the journal {Science and Culture} and was its editor until his death. He was concerned about the development of India and discussed such policies in his writings in this journal. In 1951 he won the first election in independent India as an independent and became a Member of Parliament. He did not have money, and his election campaign was funded by sales of his books and contributions from the public. Till today he remains the only scientist to have been directly elected to the Lok Sabha.

Work as a parliamentarian
In Parliament he was so forthright and clear in his comments that the Congress MPs (that government was under our first prime minister, Jawaharlal Nehru) would be terrified that he would point out their lapses. This is not to say that he was always critical. He helped in the planning of the dams in the Damodar river, which led to irrigation projects and contributed to the electrification of the states of Jharkhand and West Bengal. He did not agree with Mahatma Gandhi's ideas of a village-based economy and helped in setting up of the National Planning Committee under Netaji Subhash Chandra Bose's Congress in 1938, which after independence became the Planning Commission.

Saha and international recognition
Saha studied with Satyendranath Bose, another great Bengali physicist. The works of Bose and Saha and C V Raman were considered worthy enough of applying for the Nobel prize. Raman got the Nobel prize in 1930 for his Raman scattering effect. Saha was nominated for his Saha formula, and Bose for the Bose statistics, but they did not win the prize.
Astronomers such as Annie Cannon, Edward Pickering, Ejnar Hertsprung and Henry Russell had realized that the colours of stars were related to their absolute brightness (not their apparent brightness, which could also be because they are near us). Most of the time, blue stars are very luminous and red stars much less. (Some exceptional red stars go under the name of "red giants" and some exceptional white stars are called "white dwarfs".) Yellow stars like our Sun are in the middle. This can be seen by plotting a graph that has come to be called the {H-R diagram}, named after Hertzsprung and Russell based on the classification suggested by Cannon and Pickering. The figure shows many well-known stars in our Milky way galaxy, plotted on such a diagram.

Stars and ionisation
When observing the spectrum of a star, one can see dark lines in it which can be attributed to elements in the stellar atmosphere which absorb the radiation coming from the interior. Some elements are ionized, that is, their atoms lose electrons. In his 1920 research article, Saha used quantum mechanics to find a way of calculating the temperature of a gas when the atoms get ionized. Since the spectral line of an ionized atom can be seen with a spectroscope, from its observation we can read off the temperature of the star's surface or higher in the atmosphere. Blue stars have very hot surfaces and red stars much less so. Thus the H-R diagram can also be seen as a plot of the stars' luminosity versus temperature. That is often the meaning given to the H-R diagram today. George Hale, director of the Mount Wilson observatory which had the largest telescope at that time, refused Saha's request to obtain spectra to verify his ideas.
The same calculation was later done by American chemist Irving Langmuir in 1932. Langmuir won the Nobel prize since he had also done earlier work on gases and atomic structure, which was rated as more of a discovery.

Hydrogen and helium in the stars
In her PhD thesis in 1934, the first in astronomy from Radcliffe College in Harvard university, Cecilia Payne (later Payne-Gaposchkin) used Saha's ideas to identify the quantity of an element in the Sun, realizing that although there were many more lines in its spectrum, they were all due to the usual elements, with different ionizations. She came up with the startling conclusion that most of the Sun (and stars) was made up of hydrogen and helium. This has been called one of the brilliant PhD theses in astronomy.
One of her thesis examiners was Henry Russell. He asked her to withdraw that conclusion since it did not match the theories prevalent then (including his own, which said that Earth and Sun had the same composition). Later he realized his mistake when he derived the same result in a different way, and gave credit to Payne.

Saha as a nation builder
Saha published many other papers, co-authored two physics textbooks and wrote many popular articles. He believed in doing science in one's own language. He was the president of the Indian Science Congress in 1934. He was involved in the setting up of the UP (later National) Academy of Sciences in Allahabad, the Indian Academy of Sciences (which Raman took over) in Bangalore, the National Institute of Sciences (now called INSA) in Delhi, and the Institute of Nuclear Physics in Calcutta, which is now named after him.