The problem of solar energy generation: from Eddington to Bethe

Abstract The problem of explaining the Sun’s enormous output of heat and light was first attacked in the 1840s and soon resulted in a consensus view that solar energy was mechanical in origin. From about 1860 to 1905 the standard model was the so-called Helmholtz-Thomson contraction theory which however faced a number of serious problems. Physicists and astronomers slowly realised that the source was not mechanical but due to intra-atomic processes, either proton-electron annihilation or fusion of hydrogen into helium atoms. Both possibilities were discussed by Arthur Eddington in the 1920s, but it was only with quantum mechanics and a new picture of the atomic nucleus that quantitative models were developed. The old riddle of solar energy was essentially solved with Hans Bethe’s celebrated theory published in 1938-1939. This paper briefly reviews the developments from about 1850 to 1940.