a priori proofs that the Earth is a globe?
If the Earth was flat, we'd be able to see the Sun at all times.
If the Earth was flat we would be able to see the entire earth from an airplane..
Also, there would be no horizon.
Flat Earthers just ignore these facts and say stupid shit like light refraction and fog..
Even on a clear day the mountains in the distance appear with a blueish tint, and you want us to believe we'll see anything but pitch black on the other side of the planet presuming one had a powerful enough telescope?