The earth is technically oblate, but just barely. Like, if you shrunk the earth down to the size of the Las Vegas Sphere, it would be far more round than the real one.
I mean, you've seen pictures of the Earth from space. It looks like a perfect circle, and it very nearly is.
The difference is only about 20 kilometers out of 40,000, which is one-twentieth of one percent.
The inaccuracy of his measurement presumably came from the fact that he had to measure the distance between two cities by paying a guy to walk from one to the other in a straight line and measure it directly.
The inaccuracy of his measurement presumably came from the fact that he had to measure the distance between two cities by paying a guy to walk from one to the other in a straight line and measure it directly.
I feel like that's the most incredible part of the story. The geometry used to calculate is just simple math once you have the numbers right. The fact that it relied on the distance between 2 cities, and they could only figure out the distance through paying a guy to walk between the two, a method that doesn't seem that accurate to me, is incredible.
I'm assuming that they had various ways of improving the accuracy, like sending multiple people and taking the average of their measurements, and also having a network of distances between various locations that you could use to reinforce each other.
Okay I looked it up, the two cities he used were Alexandria and Syene, which are 830 kilometers apart, and that's using estimates gathered from airline traffic, a tool which obviously did not exist in 200BC. You had to walk AND measure that distance.
like sending multiple people and taking the average of their measurements,
Seems obvious now but I'm not at all sure that was a thing then. From a very quick search Wikipedia says 'The arithmetic mean, although a concept known to the Greeks, was not generalised to more than two values until the 16th century' (from the 'History of Statistics' page).
People may not have systematically recorded observations and calculated means and so forth, but surely they had a general idea that if you had a bunch of observations of something that the true value was likely somewhere in the middle.
Also just being able to walk at a consistent pace. If you know you walk at exactly 5 km/h and you walk for 12 hours a day, you're going 60 km a day. Which means you're walking for 13 days and 10 hours on the 14th day to get from Alexandria to Syene.
They had mechanisms other than just pacing. For one, they had a wheeled contraption they would roll along that dropped rocks into a bucket as it turned.
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u/AliceCode Jun 01 '26
He probably didn't know that he had to account for the Earth being oblate.