I worked for decades as a broadcast engineer. The formulas we use to determine the coverage of radio stations work perfectly, and are based on (among other things) the sphericity of the Earth. If the Earth were flat, FM stations from Tasmania could be heard routinely and clearly in the Hollywood hills.

We've known about the sphericity of the Earth since Eratosthenes' intelligent experiments 2200 years ago. When the Christians burned the great libraries and philosophic schools, they imposed vulgar Semitic fables on us, such as the "flat Earth." The rediscovery of European science and natural philosophy in the Renaissance got people thinking again, with Columbus's and Magellan's great voyages among the results.

Every single radio station in the world, and there are tens of thousands of them, proves that the Earth is a sphere -- as does even the most basic understanding of our intellectual heritage.