Arthur Stanley Eddington was a British Astrophysicist in the early 20th century. He studied the internal structures of stars. His book The Internal Structures Of Stars was published in 1926. In the book he suggested that nuclear reactions are the power source of stars. While, he worked at the Royal Greenwich Observatory, he led two expeditions to view solar eclipses. He became professor of astronomy of Cambridge in 1913. He proved that there is evidence for the theory of general relativity. He was born at Kendal, United Kingdom in 1882, and died at Cambridge in 1944. In 1914 he was the director of the Cambridge Observatory. He had a mass-luminosity relationship for main sequence-stars. His awards are the Gold Medal Of The Astronomical Society, Royal Medal, Bruce Medal, and The Henry Draper Award. He was a philosopher of science.