What happened today
A solar eclipse - and it was yuge.
But why is this important? Why is an eclipse that took place almost exactly a century ago have any relevance today?
Because it was the first verification of Einstein's theory of general relativity.
Part of the General Theory predicts how much matter bends space. This eclipse was designed to see if Einstein was correct about how much gravity bent space or if Newton was correct.
Sir Frank Watson Dyson, Astronomer Royal of Britain, conceived in 1917 the perfect experiment to resolve the issue. A total solar eclipse on May 29, 1919, would occur just as the sun was crossing the bright Hyades star cluster. Dyson realized that the light from the stars would have to pass through the sun’s gravitational field on its way to Earth, yet would be visible due to the darkness of the eclipse. This would allow accurate measurements of the stars’ gravity-shifted positions in the sky.From Headstuff:
Eddington, who led the experiment, first measured the “true” positions of the stars during January and February 1919. Then in May he went to the remote island of Príncipe (in the Gulf of Guinea off the west coast of Africa) to measure the stars’ positions during the eclipse, as viewed through the sun’s gravitational lens.
Eddington also sent a group of astronomers to take measurements from Sobral, Brazil, in case the eclipse was blocked by clouds over Príncipe. Outfitting and transporting the dual expeditions were no small feats in the days before transoceanic airplanes and instantaneous global communication.
Dyson presented the main results at a special meeting of the Royal Astronomical Society and the Royal Society of London on 6th November, 1919. Crommelin’s results from Sobral, with measurements from seven stars in good visibility, gave the deflection as 1.98(+/-) 0.16 arc seconds. Eddington’s results from Principe were less convincing. Measurements were taken from only five stars and due to the bad weather conditions the error was much larger. Nevertheless, they still had a result of 1.61 (+/-) 0.40 arc seconds. Both results were within two standard errors of Einstein’s predicted value of 1.74 and both were also more than two standard errors away from either zero or the Newtonian value of 0.87 arc seconds.These results have been confirmed a number of times since:
After this monumental expedition many more went on to cement Einstein’s theory. In 1922 another eclipse, viewed from Australia, produced scores of measured angles of deflection and had much more convincing statistical data. The standard error however was still of a similar size, around 0.20 arc seconds. Measuring the deflected light rays in this manner, using optical telescopes, continued into the 1950s but never increased much in accuracy. This is due to the difficulties in observing stars through our atmosphere.Ever since, Einstein's theory (and remember it's "just a theory") has been confirmed by experimental data.
It's true - horray for science!