But they don't dissappear. You can look up a number of experiments with cameras and telescopes. It's an optical illusion. For instance, you can see a ship dissappear on camera, put a telescope on said camera and boom, ship reappears. So I don't know what you're basing your observation on. The naked eye? You can only perceive so much. As an artist we call it the vanishing point. Has nothing to do with curvature and everything to do with physics and perception. Again, there are examples. How would the horizon work on flat earth? Could I see a ship a million miles away? How do you think a artist would draw that?