A giant tool in the sky - testing general relativity


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As we approach the Summer Solstice, our Curator of the Royal Observatory looks at how the sun was used nearly 100 years ago to test Einstein's theory of general relativity.  

It’s great to enjoy the sunshine and long hours of daylight at this time of year. As we approach the Summer Solstice on 21 June, it’s a timely reminder of how much we depend on the Sun for light, heat and energy. But nearly one hundred years ago, astronomers and physicists were keen to use our nearest star for another purpose – a giant scientific instrument for proving Einstein’s theory of general relativity. In his radical new idea first published in 1915, Einstein argued that the gravitational field surrounding massive objects distorted time and space around them, an effect which could even bend light. This tiny effect was too difficult to be measured in a laboratory on Earth but Einstein proposed that certain phenomena in space, such as a total solar eclipse, offered the perfect conditions to test his theory.

Astronomers across the globe realised that the approaching eclipse on 29 May 1919 offered a suitable test and two teams of astronomers from the Royal Observatory set up observing stations on the island of Principe, off the west coast of Africa and in Sobral, Brazil. Despite numerous logistical and technical challenges, the eclipse expedition was a success and it contributed to the acceptance of Einstein’s theory within the scientific community.

Eclipse of the sun, 1919, showing a great prominence. AST1093 Eclipse of the sun, 1919, showing a great prominence. AST1093


Find out more on our Summer Solstice Day on Sunday 21 June 2015 when Louise will be speaking about this historical event in more detail throughout the afternoon. You can also join our team of astronomers to view the Sun safely through telescopes set up outside.