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While World War I was tearing Europe apart in 1915, a German physicist presented a theory that would shake up the way we see the Universe. The physicist was Albert Einstein, his face still unknown to the world, his name not yet a synonym for genius. How did a solar eclipse in 1919 change all that?

Einstein's Eclipse

Here is a picture of the old plantation buildings at Roça Sundy on Principe. This is where Eddington made his headquarters when he made the eclipse expedition. I've located Principe on the map, but the Pinterest map is run by Foursquare and it doesn't know where Roça Sundy is, so the closest I could get was to find the island!

Einstein became an international celebrity after the story of the eclipse spread. He remained in the public eye for the rest of his life.

But Eddington was also well known during his lifetime. Stellar physicists would still know his name today because of the "Eddington limit," which is the maximum luminosity a star can have when it's in equilibrium. But in his day, besides his academic work, he was a science popularizer. He wrote popular science books and gave lectures to communicate scientific ideas to the public.

Eddington also achieved the ultimate 20th century accolade - in 1934 Eddington made the cover of Time magazine!

On May 29, 1919 English astrophysicist Arthur Eddington observed a solar eclipse on the African island of São Tomé and Príncipe. His results - plus those of colleagues in Brazil - confirmed an important point of Einstein's General Theory of Relativity. Both Einstein and Eddington became international celebrities.

In 2009 São Tomé and Príncipe issued a set of commemorative stamps . This is normally the sort of thing that would accompany a centenary, but 2009 was special. It was an International Year of Astronomy, so the stamps mark the 90th anniversary of the eclipse. Today is the 96th anniversary of this historic event.

A friend of mine has been busy. When "Einstein's eclipse" occurred, the background stars were in a particular position. He worked out when the Sun and background stars would be in the same positions and caught it on the SOHO website. SOHO is an orbiting solar observatory.

This is a digital image of a photographic plate Arthur Eddington took during the total eclipse. This is what SOHO saw a few days ago.

On May 29, 1919 British astronomers made a test of one aspect of Einstein's Theory of General Relativity. Einstein's theory said that massive objects curved the space around them and that light would travel along this curved path. This was tested during a total solar eclipse when stars can be seen in daylight.

This diagram explains what they would find if Einstein's theory were correct.