Key word is "appears." Brain function is another frontier of knowledge just like all those encountered in a space program. The Ponzo illusion is one possible e

Key word is "appears." Brain function is another frontier of knowledge just like all those encountered in a space program. The Ponzo illusion is one possible explanation of the Moon illusion, with objects appearing "far away" (because they are "on" the horizon) appearing bigger than objects "overhead". However, some have argued that explaining one perception ("appears far away") in terms of another ("appears bigger") is problematic scientifically, and that there are probably complex internal processes behind these illusions. https://en.wikipedia.org/wiki/Ponzo_illusion https://en.wikipedia.org/wiki/Ponzo_illusion