The Sobral's eclipse and the gravitational deflection of light predicted by Einstein

Abstract

This article is for celebrating the centennial of the total eclipse of the Sun on May 29, 1919, which observational data collected by two British teams gave rise to a remarkable milestone of the History of Science: the confirmation of the deflection of light by the Sun, predicted by Einstein, that enthroned him overnight in the pantheon of the geniuses of the mankind; and the launch of General Relativity Theory into the world. But this eclipse concerns especially to us, Brazilians, as it was observed by one of the British teams in Sobral, CE. For the good understanding of this event, the curious idea that light can stop walking straight, will be discussed from its earliest records. The formulation of this idea followed step by step the construction of the General Relativity, or rather the transition from the Restricted Relativity of 1905 to the General Relativity of 1915. The possibility of the detection during an eclipse of the deflection of light, one of the tests of the validity of the General Relativity, aroused the interest of astronomers from many countries for many years. In the eclipse of 1919 the confirmation of the deflection of light and the validation of General Relativity was boastfully announced. Again, for the good understanding, this part of this paper will be supplemented with a clarification of the technical terms and procedures for photographic observation and image analysis. The discussion and the announcement of the results and the "super-proof" of the deflection of light achieved after decades, will be discussed in the light of the studies made by astronomers and physicists, as well as historians and philosophers of science in these 100 years since the eclipse, intending to propose to the readers a reflection, not only on the conceptual and technological advances of science, but especially on the new assessments of the validity of scientific knowledge, the incidence of sociological and less rational factors in the building of this knowledge. Behind the scenes of the scientific community, the bombastic announcement of the 1919 eclipse results was not as straightforward as the headlines of the epoch and some of the current headlines still insist. The centennial is an opportunity for an amendment for the sake of a realistic and not falsely idealized perception of the science and the scientists.