Neil deGrasse Tyson Explains Why Earth Is Not Flat, Again, Says Education System Has Failed

Neil deGrasse Tyson used plain and simple science in the latest episode of his StarTalk podcast to explain why the theory that the Earth is flat is incorrect. In case one explanation wasn’t enough for viewers, Tyson used no less than three examples of experiments that prove the Earth is spherical.

First, the astrophysicist and head of the Hayden Planetarium, pointed out the flawed thinking that other planets would be spherical but not the Earth. He also explained that if something in space has a flatter shape rather than a spherical one, something, like rapid rotation, made it that way.

While sitting with his co-host for the episode, Chuck Nice, Tyson began on the first explanation. It was one that many people in the United States got a good example of in January: a lunar eclipse. To explain why a lunar eclipse means Earth must be sphreical, he first explained how a lunar eclipse works: Earth is always casting a shadow out into space and when a lunar eclipse occurs, the moon moves into that shadow.

"If you see the shape of Earth’s shadow on the moon, it is always round, always round. If Earth were flat, sometimes you’d get like a flat shadow and we’ve never seen a flat shadow," he explained.

Furthermore, he pointed out that the only shape that produces a circular shadow no matter what angle light hits it is a perfect sphere.

lunar eclipse diagram A lunar eclipse happens when the Earth moves between the sun and the moon and eclipses the moon, or blocks the sun's light from reaching it. NASA

Should that easily observed and well documented reason that the Earth is not flat isn’t enough for some, Tyson went on to explain an experiment that was done in ancient Greece by Eratosthenes. The experiment relied heavily on geometry and measurements but essentially showed that the sun’s light did not hit different parts of the Earth at the same time at the same angle. It also allowed him to measure the Earth’s circumference.

Lastly, Tyson used a simple observation.

"If you send a ship straight to the horizon eventually it begins to disappear until it’s no longer visible beyond you horizon," he said.

If the Earth were flat, the ship would never fully disappear from view.

"For me, the fact that there’s a rise of flat-Earthers is evidence of two things. One, we live in a country that protects free speech. And two we live in a country with a failed educational system," Tyson said about the lack of understanding that the world is, in fact, round.

"Our system needs to train you not only what to know, but how to think about information and knowledge and evidence."


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