When I first learned long ago that huge moon during moonrise is not optical distortion, but pure human mind produced illusion, I was quite astonished. http://www.amnh.org/naturalhistory/city_of_stars/21_full_moon.html [Broken] It is explained away by fact that for human, atmosphere above seems spherical and touching with horizon. Because we can see horizon only relatively close to us, it "seems" correct that objects at that distance must be closer that straight above. Now, because light from moon in the sky doesn't show any reduction in size, mind works it out that moon must be "as close" as sky above and as close as horizon, and it makes a "correction" due which we perceive moon literally huge. Probably many have read from books hot arguments in past between people who believed earth was flat and those who new already that its a sphere. Arguments were as simple as "walk up the hill and see yourself - its flat". I find it amusing, because as soon as I get some 20-30 feet elevation, I can immediately "see" curvature of horizon, and there is no question of such kind, at all. I can't remember how I perceived it as a child, but I know for sure that after a first flight by plane its been like that ever since. This made me really think if how we perceive reality with our eyes is strongly influenced by what we know about it? Mean, people in the past were not stupid liars, they really saw the flat earth. And we know its sphere, so we see it as a curved horizon. This mind game must be possible, as anyone who have seen huge moon on horizon can tell. But what are the limits of such influence on perception?