I once was a flat-Earth-accepter, but then I questioned that because of some individual called Johannes Kepler. I was told that his calculations (currently called "Kepler's laws of planetary motion") "proved" the Earth was a ball in a ring of other orbiting balls around the Sun. This made me unsure of the shape of the Earth for a long time, I believe five months.
During that time, I gravitated (pun unintended) progressively toward the notion that the Earth indeed is a sphere (mostly just because of Kepler).
Yesterday, I came upon