Science › Space, time & gravity
1919 eclipse: gravity bends light
1919· Discovery / experiment
ProvenTested many times; part of working physics.
Arthur Eddington's 1919 eclipse expeditions measured starlight bending around the Sun by about the amount general relativity predicted.
See it on the Science map →How it works
During a total eclipse the Sun's glare is blocked, so stars near it become visible. If gravity bends light, those stars should appear slightly shifted. Einstein predicted 1.75 arcseconds, twice the value a Newtonian argument gave. On 29 May 1919, teams at Príncipe, off West Africa, and Sobral, Brazil, photographed the stars. The results, announced in London in November, favored Einstein.
Why it matters
It confirmed that gravity bends light and made general relativity, and Einstein, front-page news worldwide.
How we know
The 1919 data were rough and some plates were discarded, which historians still debate. Later eclipses and 1970s radio telescope measurements confirmed the bending to better than one percent.
Still a mystery
How much the 1919 analysis was influenced by expectation is debated; the conclusion has been fully confirmed since.
Connections (2)
▸General relativity: gravity is curved spacetime predicted 1919 eclipse: gravity bends lightProven
The relationship
Curved spacetime bends light passing near the Sun. General relativity predicted a shift of 1.75 arcseconds for starlight grazing the Sun, double the Newtonian estimate. A total eclipse allowed the shift to be measured.
How the link was found
Einstein predicted the full value in 1915; Eddington and Dyson organized the May 1919 expeditions.
Why it's proven
The 1919 results favored Einstein; later radio measurements confirmed the value to better than one percent.
Open questions and mysteries
Debate continues over how carefully the 1919 data were handled.
▸1919 eclipse: gravity bends light made world-famous Albert EinsteinProven
The relationship
When the eclipse results were announced in London in November 1919, newspapers presented them as a revolution overthrowing Newton. Coming just after World War I, a British team confirming a German-born scientist's theory caught the public imagination. Einstein, known mainly to physicists until then, became a worldwide celebrity almost overnight.
How the link was found
Results announced at a joint meeting of the Royal Society and Royal Astronomical Society on 6 November 1919; The Times and New York Times ran headlines within days.
Why it's proven
The press coverage and Einstein's sudden fame are thoroughly documented in newspapers, letters and his lecture tours of the early 1920s.
Open questions and mysteries
Historians debate how much the fame came from the science versus postwar politics and the press's appetite for a story.