During this week in 1919, Sir Arthur Eddington profoundly changed the way we view the Universe.
Eddington watched stars near the Sun during a total solar eclipse on the African island of Principe. When the Sun was in front of the stars, they appeared to move away from their true positions, which Eddington had recorded in Oxford, three-and-a-half months earlier.
This was the first observational proof of Einstein’s theory of general relativity. Interestingly, Einstein’s first celebration was, like Eddington, to write to his mum. There must be a moral to take from this common theme.
General relativity describes how any massive object, such as the Sun, produces gravity by bending space and time around it. Everything in that space is also bent: even rays of light, and these get deflected.
Light doesn’t always travel in straight lines
Einstein’s prediction of this effect was used to determine the nature of gravity. But now that it is well understood, the effect of “gravitational lensing” has become one of the most powerful tools used by astronomers to probe the Universe.