How to Measure the Earth’s Radius With Legos

more than 2,000 Years ago, almost every educated human being knew that the Earth was round. After all, there are some pretty obvious clues. If you travel south, you see stars and constellations that you have never seen before (because they are blocked by the curvature of the Earth). When a ship arrives at port, you see the top before the bottom (because the sea surface is curved). Finally, when the Earth’s shadow falls on the Moon in a lunar eclipse, the shadow forms a circle. I mean, come on!

But this is impressive: Around 240 BC, the Greek mathematician Eratosthenes, head of the famous Library of Alexandria in Egypt, came up with a brilliant way to calculate the radius of a spherical Earth. You can do it too, and it doesn’t require any fancy equipment. I’m going to show you how to measure the size of the Earth using Lego pieces.

Of course, Eratosthenes didn’t have Legos. But he knew that at noon on the summer solstice, the sun shone directly into a vertical well in Siene, Egypt. This meant that the sun was directly overhead. So what did he do? He set a pillar in the ground in Alexandria, and that same day at noon he found that a shadow was falling on it, which meant the sun. was not Over there.

In the photo below, I’ve used a pillar in the fountain instead of a well (obviously not to scale), but it’s the same idea. You can see that if the Sun is aligned with the Cyane pole, it will not be aligned with the Alexandria pole. This can only mean that the Earth is curved. But, yes, he knew it.

Illustration: Rat Allen