Andrew Vanden Heuvel: The moon illusion

The moon illusion

Have you noticed how the full moon looks bigger on the horizon than high overhead? Actually, the two images are exactly the same size -- so why do we perceive them differently? Scientists aren't sure, but there are plenty of intriguing theories. Andrew Vanden Heuvel unravels the details of focus, distance and proportion that contribute to this mystifying optical illusion. [Directed by Kozmonot Animation Studio, narrated by Michelle Snow].

The moon appears larger on the horizon than when overhead, though its size never actually changes. This ancient puzzle has challenged thinkers from Aristotle to Da Vinci, yet no single theory fully explains it. Some illusions, like Ebbinghaus or Ponzo, offer partial answers, but even pilots and sailors see the effect with no visual cues. Scientists now suspect the way our eyes focus at different distances may shrink the moon overhead, leaving the question open and endlessly fascinating.