Einstein’s theory of general relativity is tested, May 29, 1919
The two astronomers did so while on an expedition led by Eddington to photograph the day’s total solar eclipse, one of the longest solar eclipses of the 20th century at 6 minutes 51 seconds.
Positions of star images within the field near the sun were used to verify Albert Einstein's prediction of the bending of light around the sun from his general theory of relativity.
Einstein’s theory was fairly new as he had only published it in 1916. His theories were also under much criticism at the time in Europe. The period followed on World War I and many members of scientific communities were not interested in pursuing theories from a German-born physicist.
During World War I Eddington was Secretary of the Royal Astronomical Society, which meant he was the first to receive a series of letters and papers regarding Einstein’s theory of general relativity from Willem de Sitter, a Dutch mathematician, physicist, and astronomer who worked closely with Einstein.
Eddington not only had the mathematical skills to understand general relativity, but was an internationalist and pacifist, immune to concerns of Einstein’s birthplace. He quickly became the chief supporter of relativity in Britain.
After the war, Eddington travelled to the island of Príncipe near Africa to watch the solar eclipse of May 29, 1919 (see his photo above). During the eclipse, he took pictures of the stars in the region around the sun. According to the theory of general relativity, stars with light rays that passed near the Sun would appear to have been slightly shifted because their light had been curved by its gravitational field. This effect is noticeable only during eclipses because the Sun's brightness obscures the affected stars. Eddington’s photographs showed that Newtonian gravitation could be interpreted to predict half the shift predicted by Einstein.
Although the quality of Eddington's observations were poor in comparison to later observations, they were sufficient to persuade contemporary astronomers and were hailed at the time as a conclusive proof of general relativity over the Newtonian model.
Eddington went on to lecture and spread the word, attempting to popularize relativity, across the world. He is credited as being able to speak eloquently at both layman levels and in highly scientific terms.
- Light bending in space—Kepler meet Einstein
- Albert Einstein is born, March 14, 1879
- Einstein paper outlines E=mc2, November 21, 1905
- Einstein wins 1921 Nobel Prize in Physics, November 9, 1922
- Wise words from Einstein, Tesla, Spock, and others
More from this day in tech history:
On May 29, 1999, Space Shuttle Discovery became the first shuttle flight to dock with the International Space Station.
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Editor's note: This article was originally posted on May 29, 2013 and edited on May 29, 2016.