First, Eddington was one of the few people in the world who understood general relativity. In addition, Eddington belonged to the Religious Society of Friends, and as a Quaker and pacifist, he did not participate in the war. This was crucial because the nations were still in conflict when Eddington and the UK Royal Astronomer, Frank Dyson, raised the possibility of organizing two simultaneous expeditions to observe the total eclipse of 1919. Fortunately, the First World War ended earlier. Eddington and a companion, watchmaker Edwin Cottingham, went to Prince’s Island (currently in the Democratic Republic of Sao Tome and Principe), while two other companions traveled to observe the eclipse from Sobral, in northern Brazil.
The Moon covered the Sun on the African island of Príncipe. Arthur Eddington had been preparing for the moment for months. It ran on May 29, 1919 – today a hundred years ago – and for almost seven minutes, the British astronomer was able to photograph a cluster of stars in the constellation of Taurus, visible around the eclipse. The data collected that day made it possible to verify that the light of distant stars doubles when passing by the Sun, as predicted four years earlier by Albert Einstein, a German physicist known only in expert circles. That year, just after the Great War, the theory of general relativity prevailed triumphantly over the seriousness of Isaac Newton and the world met Einstein. Science would never be the same anymore. when Einstein presented his general relativity at the end of 1915, he went unnoticed outside of Berlin. One person who did know about the revolutionary theory, thanks to correspondence with another Dutch scientist, was Eddington, then secretary of the Royal Astronomical Society in England. He had two qualities that determined the course of history.
Of the 19 astrographic plates that Eddington took, facing clouds and mosquitoes, only two were well focused. His colleagues in Brazil had better luck and returned with eight plates of higher quality for analysis. The objective was to check if the gravitational distortion of light that predicted Einstein’s theory occurred. According to general relativity, space and time form a four-dimensional tapestry that deforms in the presence of a massive object, like our Sun. Light, like matter, travels through this fabric of the universe, and its trajectory seems deviate wherever it is deformed.
Curiously, Newton’s laws governing physics since 1687 already predicted the gravitational attraction of light, but to a lesser extent. There was great interest in the new scientific theories of the twentieth century because the Newtonian gravity did not explain newly detected anomalies in the orbit of Mercury. General Relativity does, by posing gravitational attraction not as an instantaneous phenomenon, but as a consequence of spatial deformation, which propagates only at the speed of light. Eddington calculated that, if General Relativity was correct, during the eclipse exactly twice as much light distortion would be observed as following Newtonian gravity.So it was