• Moiya McTier

Astronomy Fun Fact #80

In honor of yesterday's total solar eclipse in South America, here's another eclipse fact.

One hundred years ago, Albert Einstein was looking for a way to experimentally prove his newly published theory of general relativity (which claims that gravity is actually caused by distortions in the fabric of space-time).

To test out his theory, Einstein wanted to show that a massive object can actually distort this fabric enough to bend the path of light. But he needed a truly massive object for the effect to be observable, and the most massive object nearby is the Sun.

Einstein and some other leading scientists from the time thought that they'd be able to observe the light from background stars get bent due to the Sun's gravity. The problem was that those stars were invisible during the day because they were blocked by the Sun's glare.

But in 1919, a total solar eclipse was visible from the southern hemisphere and the moon blocked enough of the Sun's light that those background stars were visible during the day. Einstein and his team were then able to compare the actual position of the background stars to their apparent position after their light was bent by the Sun's gravity.

The difference between where the stars appeared to be and where they actually were proved that the light's path was being distorted by the Sun's gravity. And that made Einstein the most famous physicist of the 20th century.

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