Friday, May 27, 2011

Moon Size Illusion (Solstice)

The full Moon beams through trees in Manchester, Maryland. Credit: June 16 , 2008 Edmund E. Kasaitis. Copyright 2008; all rights reserved

  • The Moon illusion is an optical illusion in which the Moon appears larger near the horizon than it does while higher up in the sky. 
  • This optical illusion also occurs with the sun and star constellations. 
  • It has been known since ancient times, and recorded by numerous different cultures. The explanation of this illusion is still debated

Moon Size Illusion - 2 Main Theories
1.The Ponzo Illusion

Two yellow bars are drawn across railway tracks which converge towards the distant horizon.
To the eye, the top bar appears to be wider than the bottom bar.
In the same way, with a low-lying moon the trees and houses, which are familiar foreground reference points, appear smaller against the moon, which appears bigger than it really is.
Sceptics of this theory point to airline pilots who also see the illusion, although they have no ground reference points
2.Alternate View
The brain perceives the sky as a flattened dome rather than the true hemisphere it really is.  

Maybe it's the shape of the sky. Humans perceive the sky as a flattened dome, with the zenith nearby and the horizon far away. It makes sense; birds flying overhead are closer than birds on the horizon. When the moon is near the horizon, your brain, trained by watching birds (and clouds and airplanes), miscalculates the Moon's true distance and size.

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