It started with Eratosthenes who realised that there was a particular well that the sun illuminated all the way to the bottom on a particular day. He knew that on this particular day, another well of another town did not have the sun directly above it.
He then realised that if he placed a few sticks on the ground and measured the difference in shadow angle, he could work out the circumference of the world.
Flat earthers will tell you that you can get the same effect with two sticks on a flat plane; what they don't tell you is that you can't recreate the same thing with 3 sticks, and thus the theory breaks down again.
It started with Eratosthenes who realised that there was a particular well that the sun illuminated all the way to the bottom on a particular day. He knew that on this particular day, another well of another town did not have the sun directly above it.
He then realised that if he placed a few sticks on the ground and measured the difference in shadow angle, he could work out the circumference of the world.
For a much better explanation :-) check out this link http://www.dummies.com/education/math/geometry/how-to-determine-the-earths-circumference/
Flat earthers will tell you that you can get the same effect with two sticks on a flat plane; what they don't tell you is that you can't recreate the same thing with 3 sticks, and thus the theory breaks down again.
Cg