Starting On The GroundOne of the ways the ancient Greeks concluded the Earth is spherical was by observing ships on a horizon. This illusion happens because the ship is moving further along the curve of the Earth. We have several components of an equation, courtesy astrophysicist David Lynch, that can be used to calculate the curvature of the Earth. Alternatively, if we take the radius of Earth for granted (and trust what’s already been proven) we can also determine the Earth’s radius. Seeing any observable curvature from a plane is difficult for several reasons:Airplane windows distort light coming into the plane, in other words, they add a curvature effect not too unlike a wide-angle lens.