The moon illusion - why does it look so much bigger on the horizon?

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.

Originally published on TEDed: