The Moon Illusion refers, roughly speaking, to the common experience that the moon appea it is near the horizon than when it is at its zenith. To investigate, we have designed an exper must adjust the diameter of a variable circular light placed at eye level to match the diamete well above eye level. (See, for example, Kaufman, L. & Rock, I. (1989), "The moon illusion t M Hershenson (Ed.) The Moon Illusion, Hillsdale, NJ: L. Earlbaum.) We have tested 28 participants and recorded for each participant her experimental "adjustabl summarized in the following histogra