For thousands of years, one scientific puzzle has fascinated and perplexed the greatest philosophers, mathematicians, physicists, and psychologists - why do the moon and sun appear so much larger on the horizon than when high up in the sky? Now, two leading psychologists have provided a compelling account of this fascinating illusion. Taking us through the history, the characters involved, the attempts made to explain the illusion, through to modern day studies of visual perception, the book is the most comprehensive account of this puzzle so far. This is a work which will remain, for some time to come, the definitive book on a mystery that has fascinated and tested the greatest minds throughout the ages. Accessibly written, it will appeal to readers of popular science, along with those within the disciplines of psychology, mathematics, astronomy, and philosophy, from undergraduate upwards.