Greater than 2,000 years in the past, just about each educated human knew the Earth was spherical. There are some fairly apparent clues, in spite of everything. In case you journey south, you see stars and constellations you’ve by no means seen earlier than (as a result of they’re blocked by Earth’s curvature). When a ship comes into port, you see the highest of it earlier than the underside (as a result of the ocean floor is curved). Lastly, when Earth’s shadow falls on the moon in a lunar eclipse, the shadow is a circle. I imply, c’mon!
However that is spectacular: Round 240 BC, the Greek mathematician Eratosthenes, head of the well-known Library of Alexandria in Egypt, got here up with a superb strategy to calculate the radius of the spherical Earth. You are able to do it too, and it doesn’t require any fancy gear. I’ll present you measure the Earth’s dimension utilizing Lego items.
In fact, Eratosthenes didn’t have Legos. However he knew that at midday on the summer time solstice, the solar shone straight down a vertical effectively in Syene, Egypt. This meant the solar was immediately overhead. So what did he do? He caught a pole within the floor in Alexandria, and at midday on the identical day he discovered that it solid a shadow, that means the solar wasn’t overhead there.
Within the image beneath, I’ve used a pole in Syene (to not scale, clearly) as a substitute of a effectively, however it’s the identical thought. You may see that if the solar is in keeping with the Syene pole, it received’t be in keeping with the Alexandria pole. This might solely imply the Earth is curved. However, yeah, he knew that.
Illustration: Rhett Allain
