10 easy ways you can tell for yourself that the Earth is not flat

This story was originally published on Smarter Than That in 2008. We are republishing a lightly edited version on Popular Science in light of recent interest in the subject.

Humanity has known Earth is round for a few millenia, and I’ve been meaning to show more methods that prove the world is not flat. I’ve had a few ideas on how to do that, but recently got an interesting incentive, when Phil Plait, The Bad Astronomer, wrote about a recently published BBC article about “The Flat Earth” society. (Most recently, rapper B.o.B. went on a Twitter rant on the topic.) Phil claims it’s ridiculous to even bother rebutting the Flat Earth Society—and I tend to agree. But the history of our species’ intellectual pursuit is important and interesting. You don’t need to denounce all science and knowledge and believe in a kooky conspiracy theory to enjoy some historical factoids about humanity’s quest for space.


Now that humanity knows quite positively that the Moon is not a piece of cheese or a playful god, the phenomena that accompany it (from its monthly cycles to lunar eclipses) are well-explained. It was quite a mystery to the ancient Greeks, though, and in their quest for knowledge, they came up with a few insightful obse
rvations that helped humanity figure out the shape of our planet.

Aristotle (who made quite a lot of observations about the spherical nature of the Earth) noticed that during lunar eclipses (when the Earth’s orbit places it directly between the Sun and the Moon, creating a shadow in the process), the shadow on the Moon’s surface is round. This shadow is the planet's, and it’s a great clue about the spherical shape of the Earth.

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