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Eddington, Sir Arthur (Stanley)

star stars pressure sun’s

(1882–1944) British astrophysicist: pioneered the study of stellar structure; and discovered mass–luminosity relationship.

Eddington was the son of the head of a school in Cumbria where, a century earlier, D ALTON had taught. He was an outstanding student at Manchester and then at Cambridge, where he later became Director of the Observatory. The internal structure of stars is an area of study pioneered by Eddington. In 1926 he demonstrated that, in order to remain in equilibrium, the inward gravitational pressure of a star must balance the outward radiation and gas pressure. He realized that there was consequently an upper limit on the mass of a star (of about 50 solar masses), because above this the balance between gravitation and radiation pressure could not be achieved. (Some stars, verging on instability, pulsate; these are the Cepheid variables.) He discovered the mass–luminosity relationship, which shows that the more massive a star the greater its luminosity and which allows the mass of a star to be determined from its intrinsic brightness. Eddington provided some of the most powerful evidence for the theory of relativity by observing that light from stars near to the Sun’s rim during the total solar eclipse of 1919 was slightly deflected by the Sun’s gravitational field in accordance with predictions.

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