The earliest mention of the moon illusion we know of was impressed almost 3,000 years ago, in cuneiform script upon a clay tablet, when it was housed in the royal library of Nineveh.4 Later on, in the second century A.D., Ptolemy argued that it was the result of the magnifying properties of the atmosphere's moisture and haze. "It is just like the apparent enlargement of objects in water, which increases with the depth of immersion," he wrote.5 On account of something like divine authority, this physical or "refraction" account of the problem went unchallenged for more or less 1,000 years, a real shame since he also had an alternative physiological account that went largely ignored until Newton's time.6