How do they find out the diameter/radius of the Earth?
A few ways….you can figure it out by the arc of the horizon, as was done before Columbus (not everyone thought the earth was flat). That will give you a fairly good answer. I think someone did it by measuring the length of a shadow from a stick placed in the ground the same way in different locations (the shadow angle changes at as you move away from the equator, etc.) and that gave them the dimensions of the arc, etc….They can also calculate it by measuring the speed that earthquake waves travel through the core, and around the crust (they travel at different speeds) Since you know how far away a place is…say China…and the waves through the earth hit after a certain time, and the surface waves hit some time later, you can calculate the diameter…fun math though…lots of other ways, but there are some…
