[DuncanWaring]

As a thought experiment I tried to come up with irrefutable proof the world is round.

How about the fact that it casts a curved-edge shadow during lunar eclipses?

How about the fact that the North Star distance above the horizon depends on how far from the equator you are?

Use the Altitude of Polaris to Find Latitude.

[familyop]

"How about the fact that the North Star distance above the horizon depends on how far from the equator you are?"

Everyone south of our southern border is part of the conspiracy. They're lying, when they claim that they can't see Polaris.

;-)

[familyop]

It’s also possible that there is no southern hemisphere, and that people claiming to have been there are lying. ;-)

[stormhill]

How about the fact that it casts a curved-edge shadow during lunar eclipses?

Well, no. That could be a round disk and still be flat; no getting around the need to prove a sphere.