August 28, 2017
The Moon Delusion
Originally published February 9, 2008
image by Chris Kotsiopoulos
The orange glow and the horizontal cloud demonstrate that the left image was taken when the Moon was near the horizon. And the right image from 8 hours later was acquired with the Moon high in the sky. The two horizontal lines bracket each image almost exactly equally, showing that the Moon was the same diameter. Of course the Moon is physically the same size, but many people have had the feeling on seeing a full Moon rise that it is huge, bigger than normal. Its comforting to know that although psychologists have been studying this illusion for more than 100 years, no one completely understands why we perceive it. The comfort doesn't imply incompetence of psychologists but an acknowledgment that such a simple and commonplace phenomena is still unexplained. Our minds are far more mysterious than the Moon. A question: Is there a Moon illusion when the third quarter rises, or does it only occur with the circular full Moon? An observation: I observed a Pleiades illusion, seeing the small clump of stars as being larger than expected when rising over the clear Arizona desert - has anyone detected other size illusions associated with risings?
When I lived in Kenya I learned of a tribe that believed the dark splotches on the Moon were where people went when they died. Yesterday morning a new spot was added when lunar scientist Gordon McKay from Johnson Space Center very unexpectedly died. Gordon studied the detailed chemistry of lunar samples, and was a kind and gentle person.
Added Feb 12: Here is a remembrance of his life.
Wikipedia's Moon Illusion page
Yesterday's LPOD: Humor Me Once More
Tomorrow's LPOD: Airy Swirl