Luminance and the Moon Illusion

An investigation was made to determine if the moon illusion was caused by a change in luminance or because of a change in contrast with the sky background. Two moons, apparently equal in size, were projected to two different levels and at the same level in the sky. The horizon moon appeared to be larger regardless of its luminance, when compared to an upper moon. Nearness of the moon, to the terrain appears to affect the apparent size of the moon more than the luminance of the moon or its contrast with the sky background.