Horizontal Moon

Perhaps the most stable standing scientific puzzle is the moon illusion. Why does the moon look larger on the horizon than it does when it is higher in the sky? This puzzle, which is still unsolved, has withstood every major scientific revolution in history. However much we've progressed, we've never gotten any traction on it. We have, of course, eliminated certain solutions. We know, for instance, that the moon is not actually closer at the horizon; so it's not an astronomical phenomenon. We know that Aristotle was wrong in thinking it an atmospheric phenomenon. So we've made progress toward solving the problem; we've just never solved it. And so it is to this very day. You can read Berkeley's solution in his Essay Toward a New Theory of Vision. Berkeley's actual solution is almost certainly wrong, but NTV gives us the first truly modern apparatus for explaining the phenomenon; and virtually all attempts since have taken Berkeley's general approach of appealing to distance and size cues.