Eddington, Arthur Stanley (1882-1944)

English astrophysicist who studied the motions, equilibrium, luminosity, and atomic structure of the stars. In 1919 his observation of stars during a solar eclipse confirmed German-born US physicist Albert Einstein's prediction that light is bent when passing near the Sun, in accordance with the general theory of relativity. In The Expanding Universe (1933) Eddington expressed the theory that in the spherical universe the outer galaxies, or spiral nebulae, are receding from one another.

Eddington discovered the fundamental role of radiation pressure in the maintenance of stellar equilibrium, explained the method by which the energy of a star moves from its interior to its exterior, and in 1924 showed that the luminosity of a star depends almost exclusively on its mass - a discovery that caused a complete revision of contemporary ideas on stellar evolution.

Eddington was born in Kendal, Cumbria, England, and educated at Owen's College, Manchester, and Cambridge University. He was chief assistant at the Royal Observatory, Greenwich 1906-13, led an expedition to Malta in 1909 to determine the longitude of the geodetic station there, and went to Brazil as the leader of an expedition to observe a total solar eclipse in 1912. At Greenwich his work was mainly concerned with the analysis of stellar proper motions (the apparent movement of a star in the celestial sphere, determined by the actual movement of the star in space and the movement of the Sun), which were then just beginning to be available in reasonable numbers.

In 1913, Eddington returned to Cambridge as professor of astronomy, and was director of the university's observatory from 1914. Here his first care was to complete the meridian observations begun by his predecessor. His first book, Stellar Movements and the Structure of the Universe (1914), introduced the subject of stellar dynamics. He also became interested in Einstein's theories of relativity, and realizing that the total solar eclipse on 29 May 1919 was an opportunity to test one of its crucial predictions, accompanied the expedition that successfully confirmed it. His work on the theory of relativity was summed up in Report on the Relativity Theory of Gravitation (1918), The Mathematical Theory of Relativity (1923), and, in a slightly more popular form, Space, Time and Gravitation 1920. From 1930 he worked on the relationship between the theory of relativity and quantum theory, in Relativity Theory of Protons and Electrons (1936), Philosophy of Physical Science (1939), and the posthumous Fundamental Theory (1948).

Another subject that attracted his attention was the physical nature of the stars. In a series of papers from 1916 he developed a consistent theory of the structure of stars in radiative equilibrium, which is brilliantly expounded in the classic The Internal Construction of the Stars (1926), and, in popular form, in Stars and Atoms (1927). This work on stellar constitution initiated the researches that now form a large part of astrophysics.

Eddington's interest then turned towards the problem of the expanding universe, suggested partly by theories of relativity and partly by Hubble's discovery of the recession of the extragalactic nebulae. This led to a number of papers and The Expanding Universe; it also seems to have turned Eddington's thoughts towards philosophy. He was a Quaker, and his religious outlook is set out in Science and the Unseen World, the Swarthmore Lecture for 1929, and at greater length in The Nature of the Physical World, based on the Gifford Lectures he gave in Edinburgh in 1927.

Eddington was elected Fellow of the Royal Society in 1914 and was president of the International Astronomical Union 1938-44.