One total solar eclipse changed physics forever – and even to this day these celestial phenomena are astonishing viewers and teaching us crucial lessons about the universe
By Leah Crane
5 April 2024
A total solar eclipse from August 2017 seen above Jefferson City, Missouri
(NASA/Rami Daud)
The following is an extract from our monthly Launchpad newsletter, in which resident space expert Leah Crane journeys through the solar system and beyond. You can sign up for Launchpad for free here.
It was 1919 when the moon did a perfectly natural thing – blocked our view of the sun – and changed our understanding of the universe forever. Astronomer Arthur Eddington was watching from the African island of Príncipe, observing the positions of stars and planets that became visible during the eerie daylight darkness. With most of the sun’s light dimmed, he was able to see how light from distant stars warped as it was deflected by our sun’s gravitational pull, an effect called gravitational lensing.
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He confirmed his sightings with those of another expedition in Brazil, and these observations offered some of the first proof for Albert Einstein’s relatively new theory of general relativity. This description of how massive objects warp the fabric of space-time is now considered foundational, but at the time it was a revelation. It changed everything about how we think about gravity and the cosmos.
It also resulted in my favourite newspaper headline of all time, published in The New York Times later that year: “LIGHTS ALL ASKEW IN THE HEAVENS; Men of science more or less agog over results of eclipse observations. EINSTEIN THEORY TRIUMPHS Stars not where they seemed or were calculated to be, but nobody need worry.”
“Nobody need worry” might seem a bit over the top, but watching a total solar eclipse can indeed make you feel inexplicably nervous. I saw my first one in 2017. It was absolutely unforgettable. You might think that an eclipse is just like an overcast day with a cloud drifting in front of the sun – after all, what’s happening is simply the moon passing in front of the sun and casting a shadow on Earth – but it’s astonishingly different.