The 29th of May 1919 was the day in which the 1919 total solar eclipse occurred. A team of British scientists travelled to some of the most remote areas on earth in order to view this eclipse along it's path of totality and complete an experiment that had never been done before.
The purpose of this experiment was to prove which theory better explained the physical nature of the universe - the classical theory of the celebrated Sir Isaac Newton which had been accepted and established for around 3 centuries or the new proposal from Albert Einstein, at this point a relatively unknown German scientist.
The experiment that was carried out is explained in detail here. Basically they took photos of the position of certain stars during the eclipse and compared this to their normal apparent position in the sky. They were measuring a phenomenon known as gravitational lensing, which is essentially how light bends when subjected to a gravitational force. Einsteinian Theory predicted a deflection that was double the size predicted by Newtonian Theory.
The results obtained from observing the solar eclipse from both Principe, Africa and Sobral, Brazil concluded that the Theory proposed by Einstein was closer to what had been measured. This conclusion lit the scientific world on fire and forced us to redefine our understanding of the universe.
This experiment, which was undertaken by British scientists to prove a German scientist correct, at the expense of a British legend, was obviously controversial! Due to the fact that it occurred during the aftermath of WW1 made it appear to be more of an experiment in global diplomacy through science. This experiment, therefore has been repeated approximately 7 times since 1919, with the most recent being by Don Bruns in 2017, with the majority of the results confirming Eddington's original conclusion - that Einstein's Theory is a better fit with what is observed than Newton's.
Some of the predictions made by Einstein's Theory are still to be proven today. The discovery of the existence of gravitational waves in 2015 was a continuation of Einstein's Theory and earned those scientists a Nobel Prize!
Right now is a super exciting time in space research!! New planets, stars and entire galaxies are constantly being found as modern technology becomes more powerful, NASA recently unveiled its plan for getting people to Mars and thanks to the modern research of gravitational waves we can finally start to get more information about black holes and their function in the universe. Watch this space guys - things are only just starting to warm up!