My favourite puzzle for a flatty:
In the Northern Hemisphere anyone can go out with a camera on a clear night, point it northwards and take long exposure photos of star trails like this
which appears to show rotation around Polaris, the pole star. If the Earth isn’t spinning then is it the sky/dome that spins?
In the Southern Hemisphere you can’t see Polaris in the night sky. Which seems a bit odd. But you can see the Southern Cross. And taking a star trail photo there shows rotation around Sigma Octantis instead:
If the rotation is just due to the dome spinning, then how is it spinning around two different points at the same time?
And why can everyone towards the outer edge of the disc-Earth see the Southern Cross, but not Polaris?