Since Neil deGrasse Tyson’s big claim to fame is how he can break down astrophysics into laymen’s terms, he’s had to address the claim that Earth is flat on more than one occasion for the laymen who believe it.
This time, as the flat-earther conspiracy continues to circulate among folks who believe the Moon landing was faked and folks who don’t believe in gravity, Tyson released a longer explanation describing ways people can see for themselves how the Earth is round. The easiest way is to see the many photos of the Earth taken from space, but there are ways to do it from the Earth’s curved surface as well.
You can see his full explanation in Tyson’s StarTalk video below:
The first test involves watching a lunar eclipse. A lunar eclipse is caused when the Earth is directly blocking the Moon from sunlight, and the Moon is sitting in the Earth’s shadow. This means the shadow of the Earth is visible on the Moon, and a clearly round shape can be seen while the Moon is entering and leaving the eclipse. If the Earth was disk-shaped, we would see a disk shape on the Moon during lunar eclipses, and this has never happened.
The second test involves three wells. If a well is deep enough, it would only be possible to see the bottom of the well at noon when the sun is directly overhead – otherwise, the sunlight would be coming down at an angle that wouldn’t reach the bottom of that well. With three wells in different locations, the angles of incoming sunlight would all be different and can be measured to suggest a curved Earth.
And then there’s the much more straightforward argument that if you watch a ship sail off, you’ll eventually see it disappear into the horizon, and it would only disappear from view if it’s moving on a round surface.
As always, it’s difficult to tell whether a scientific explanation will convince any flat-earthers, when an insecure need to feel more knowledgeable than scientists is part of what fuels those flat-earth beliefs in the first place. But it may encourage anyone on the fence to try out Tyson’s tests for themselves and see the results.
And it’s another excuse to check out the next lunar eclipse when Earth blocks the Moon.