Why does the moon look bigger at the horizon? The curious case of perceptual magnification

Kalanit Grill-Spector · April 10, 2026

Have you ever wondered why the moon looks bigger at the horizon than when it is high up in the sky? This question has puzzled philosophers, astronomers, and psychophysicists for over 2 millennia. However, despite many theories, the answer to this question is a mystery. In fact, it is unknown (i) if observers perceive the moon to be larger than its actual size on the horizon or perceive it shrunken than its actual size when elevated, and (ii) if deviations in perceived size are unique to the moon (after all it is a distant (~384,400 km) extraterrestrial body). To answer these questions, we ran a series of psychophysics experiments in the wild on more than 300 participants. En route to solve this age-old mystery, we discovered a new phenomenon – perceptual magnification – and derive a new law of psychophysics – the law of perceptual magnification. Specifically, we find that (i) while the perceived magnification of the moon decreases with elevation, it is perceptually magnified both at the horizon and when elevated, (ii) perceptual magnification is not unique to the moon – observers perceptually magnify all distant objects even though they are generally unaware of it, and (iii) perceptual magnification is larger for smaller objects, more distant objects, and for objects closer to the horizon. We show that a power law with 3 factors: visual angle, distance, and elevation predicts observers’ perceptual magnification of everyday objects at distances ranging from 15-150m and all the way to the moon. While it is unsettling that we misperceive the size of distant objects, we suggest that perceptual magnification may have ecological utility for generating size constancy.