The flat earth idea has trouble explaining the horizon. How is it that we can see the sun set over a body of water and see the upper part of the sun but not the lower part? If the sun were hovering over the earth and moving away from us, we would be able to see the whole thing until it disappeared, or in other words, if it disappeared, it would all disappear at the same time (although why it would disappear at all seems to be another problem, since it is hard to see why a ball of fire would become invisible by moving a few thousand miles away from the observer on a flat surface, when it is already 98,000,000 miles away and seems to be pretty easy to see at that distance. Sorry I should have made this another paragraph maybe).