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Saha, Meghnad

metal lines temperature atoms

(1894–1956) Indian astrophysicist: demonstrated that elements in stars are ionized in proportion to their temperature.

The son of a small shopkeeper in Dacca, Saha was educated at Presidency College, Calcutta and afterwards visited Europe. He taught at the University of Allahabad and in 1938 he was appointed professor of physics at Calcutta. The absorption lines in the spectra of stars vary widely, with some showing only hydrogen and helium lines and others showing numerous metal lines. In 1920 Saha demonstrated that this did not necessarily represent a true variation in elemental composition, but a different degree of ionization of the metal atoms, which was related to temperature by Saha’s equation for a monatomic gas. At higher temperatures the metal atoms exist only in ionized form and the absorption lines of neutral metal atoms become very weak. The proportions of the various ions of the same metal can be used to estimate stellar temperature used Saha’s results to estimate the amount of hydrogen in the Sun.

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