Podcaster: Jay Pasachoff
Title: The Centennial of the Eddington Eclipse Expedition that Tested Einstein’s General Relativity
Organization: Williams College and Caltech
Description: To test Albert Einstein’s prediction, with his General Theory of Relativity, with observations from the total solar eclipse of May 29, 1919, observers led by Arthur Eddington went to Principe, now off the coast of Gabon; Cromellin led a similar expedition to Sobral, Brazil. The analysis was coordinated by Frank Dyson, the Astronomer Royal. When the results, announced a few months later, confirmed Einstein’s prediction, General Relativity became accepted and Einstein became a celebrity.
Bio: Jay Pasachoff is Field Memorial Professor of Astronomy at Williams College and Chair of the International Astronomical Union’s Working Group on Eclipses. He is on sabbatical at Carnegie Observatories.
The fifth edition of his textbook The Cosmos: Astronomy in the New Millennium (Pasachoff and Alex Filippenko, and a new book on the intersection of art and astronomy, Cosmos: The Art and Science of the Universe (Roberta J. M. Olson and Pasachoff), have just been published.
Bio: Jay Pasachoff is Field Memorial Professor of Astronomy at Williams College and Chair of the International Astronomical Union’s Working Group on Eclipses. He is on sabbatical at Carnegie Observatories. The fifth edition of his textbook The Cosmos: Astronomy in the New Millennium (Pasachoff and Alex Filippenko, and a new book on the intersection of art and astronomy, Cosmos: The Art and Science of the Universe (Roberta J. M. Olson and Pasachoff), have just been published. See http://solarcorona.com
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Today is May 29th, 2019, the 100th anniversary of the centennial of what was perhaps the most significant total solar eclipse in history– May 29th, 1919–when Arthur Eddington and others went to test Einstein’s new general theory of relativity. Here is a picture of a total solar eclipse and Einstein had predicted that during a total solar eclipse, when the stars were out in the daytime, the stars that passed near the sun (the light that passed near the sun coming toward us) would be bent, deflected. Here is a picture of Einstein visiting Caltech somewhat later on and he had written to the famous solar astronomer George Ellery Hale to see if his idea could be tested and could there be a star that went near enough to the sun and the sun would be warping space in Einstein’s new theory. So, the line at which the star would come to the earth, would–if traced back–would be slightly different than it actually is.
In 1919, there was an eclipse of the sun in which the sun was in the Hyades; there were a lot of stars close to the sun. And here is the letter from Einstein to Hale (parts of the letter) asking if his idea could be tested at an eclipse. They first tried testing it at an eclipse in 1914 and when a German scientist went in to Russia to go to Crimea to test it, war broke out, what we call World War I. The scientists were interned, their equipment was seized, and they did not succeed in making the observations at the 1914 eclipse. That was actually fortunate because Einstein only had his theory partially determined then. And, had the 1914 measurements been made, it would’ve given an answer that differed from Einstein’s prediction. It would have seemed debunked and if he fixed it up later, it would have looked like a patch.
But, as it was, they had to wait until the 1919 eclipse and when those results were released at a joint meeting of the Royal Society and the Royal Astronomical Society in November of 1919, Einstein became a worldwide celebrity. It also marked a test by British scientists of a German scientist’s idea, so it was a very ecumenical thing for the period following World War I.
In any case, the test at eclipses worked pretty well but not all the equipment worked perfectly there were some out-of-focus cameras. There were two sites. Eddington himself was in Principe, off the coast now what’s now Gabon in Africa, and Crommelin and an assistant were in Sobral in Brazil. The results were supervised when the plates were analyzed by the Astronomy Royal, Frank Dyson. It was really Dyson who gave his imprimatur to selecting which data were good enough to consider, something we are still fighting over a little bit. But Eddington has been vindicated in the eyes of the experts and the results from the May 29, 1919, eclipse have been taken to verify Einstein’s theory of relatively.
Now, Einstein had his theory tested in a number of other ways. In 1922, there was another eclipse with an even better result.
There were a series of observations at eclipses over the years. These are some oil paintings made by an artist [Howard Russell]; Butler, of the Eclipses of 1918, 1923, and 1925, because the cameras at the time couldn’t give as good an image of what the corona actually looked like as an artist could with notes taken in a couple of minutes of totality.
It does get very dark. Here is a plate that I took at an eclipse showing that it is really dark in the sky overhead even though it’s the middle of the day. This is from the book on “The Sun,” of which I am a co-author [Leon Golub and Jay Pasachoff, The Sun, 2019, Reaktion Press] and the eclipse tests have been very important for relativity over the years. But now we have a number of other tests besides the eclipses; in particular, recently, we have had the discovery of gravitational waves first by Joe Taylor and Russell Hulse in a binary pulsar, and then recently the direct detection of gravitational waves by the Laser Interferometer Gravitational-Wave Observatory, the LIGO. That is continuing; LIGO results are just picking up the gravitation waves from mergers of black holes and neutron stars, so there is no doubt now of the test of relativity.
But the celebration we have now of the centennial of the May 29, 1919, total solar eclipse observations is a very significant one and led to our current ideas about relativity and Albert Einstein and the brilliance of science.
End of podcast:
365 Days of Astronomy
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