Moon illusions redescribed

Abstract

The common report that the horizon moon looks "larger and closer" than the zenith moon means that the perceived visual angle (V′ rad) for its diameter is greater, the perceived distance (D′ m) to it is less, and the perceived linear size (S′ m) for its diameter is either greater or the same (size constancy), all in accord with the rule S′/D′ =V′ rad. These majority moon illusions remain unexplained because published descriptions use only one "perceived size" variable, rather than both V′ and S′; and some create paradoxes by using the standard rule, S′/D′ =V rad, which omits V′. Complete paradox-free redescriptions are offered, and the oculomotor explanation is outlined. © 1986 Psychonomic Society, Inc.