Which observation earned Arthur Eddington a leading role in confirming Einstein’s general relativity in 1919?

The deflection of starlight earned Arthur Eddington a leading role in confirming Einstein’s general relativity in 1919.

During a total solar eclipse on 29 May 1919, expeditions observed stars near the Sun’s apparent position. General relativity predicted that the Sun’s gravity would bend their light, making them appear slightly displaced. Eddington helped organize and analyze observations from Sobral in Brazil and the island of Príncipe.

The results were announced in London later in 1919 and made Einstein internationally famous. The observations were consistent with the predicted deflection, although later historians have discussed the limitations and uncertainties of the measurements.

Eddington did not win a Nobel Prize for this observation. The question concerns a Nobel science topic through the prize-winning theory it helped test, while avoiding the common error of calling Eddington the discoverer of general relativity. Einstein received the 1921 Physics Nobel for the photoelectric effect, not relativity.