The story
On May 29, 1919, a total solar eclipse darkened the sky over parts of Brazil and West Africa. Two British teams went to watch it: Charles Davidson and Andrew Crommelin to Sobral, Brazil, and Arthur Eddington to the island of Principe, off West Africa. Their goal was to photograph stars close to the Sun and measure whether their positions shift. Einstein's general theory of relativity predicted that gravity bends light, shifting these stars by about 1.75 arcseconds, twice the value from a simple Newtonian calculation.
Astronomer Royal Frank Dyson had noted that this eclipse would pass in front of the bright Hyades star cluster, ideal for the test, and the Royal Society and Royal Astronomical Society backed it. With the war over, the expeditions sailed in March 1919. Clouds nearly spoiled Eddington's observations. Back in England, the teams measured their plates and reported results close to Einstein's number, with the clearest Sobral instrument giving about 1.98 arcseconds and Principe about 1.6. At a joint meeting in London on November 6, 1919, Dyson, Eddington and others announced that the results favored Einstein.
The announcement made front pages: the Times of London headlined a revolution in science and the overthrow of Newtonian ideas. Einstein became a global celebrity overnight. Later work questioned how Eddington treated some data, but modern measurements with eclipses, radio telescopes and gravitational lensing have confirmed the effect with great precision.
Why it mattered
- Gave general relativity its first major experimental support, and made Einstein world famous.
- Established gravitational light bending, later used in gravitational lensing to study dark matter and distant galaxies.
- Became a model of a prediction tested by a dedicated expedition, setting a pattern for later astronomy.
- Showed science crossing the lines of a recent war, with British observers testing a German theory.
Sources
- Observing relativity Royal Society
- Bending space-time: a commentary on Dyson, Eddington and Davidson (1920) Philosophical Transactions of the Royal Society A
- Not Only Because of Theory: Dyson, Eddington and the Competing Myths of the 1919 Eclipse Expedition arXiv (D. Kennefick)
- Did Researchers Cook Data from the First Test of General Relativity? Scientific American
- The Legacy of Einstein's Eclipse, Gravitational Lensing arXiv
Contested history
Consensus: The 1919 eclipse plates favored Einstein's prediction over Newtonian bending, and later measurements confirm Einstein with high precision.
- The Legacy of Einstein's Eclipse, Gravitational Lensing arXiv
- Bending space-time: a commentary on Dyson, Eddington and Davidson (1920) Philosophical Transactions of the Royal Society A
- Did Researchers Cook Data from the First Test of General Relativity? Scientific American
- Not Only Because of Theory arXiv (D. Kennefick)
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