It's a rather enlightening exercise to work out how and why the earth is curved purely from the perspective of a human able to see maybe a small patch. This is

It's a rather enlightening exercise to work out how and why the earth is curved purely from the perspective of a human able to see maybe a small patch. This is directly analogous to how general relativity models spacetime as being intrinsically curved, and you need to be able to do the same sort of thinking without being able to immerse the manifold in a higher dimensional space. So it's not exactly stupid to pretend to be naive. Also, why and by how much is the sun bigger than the moon? How far are they away from earth? We've known for thousands of years. It's not exactly obvious to derive this purely from geometry.