Moon Illusion


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The illusion that the full moon appears larger when seen near the horizon—because perspective is provided by buildings, trees and other landscape—and smaller when seen near its zenith
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Desaguliers' experiments on apparent size were stimulated by his speculations on the link between size and distance perception in the moon illusion.
Our results leave no doubt that perceived-distance information plays a primary role in creating the moon illusion," Lloyd Kaufman says.
This is the strongest evidence so far that the perceptions of size and distance are both involved in the moon illusion," says psychologist Julian Hochberg of Columbia University.
In The Mystery of the Moon Illusion (Oxford University Press, 2002), two academic psychologists, Helen Ross and Cornelis Plug, remind us that the size illusion distorts other things in the sky.
Ross and Plug regard the effort to understand the Moon illusion via a flattened-dome sky as a fool's errand, but since we do see the sky that way they acknowledge that the flat-sky illusion deserves an explanation.
In an article published in the September 2001 Griffith Observer, astronomer Arthur Young allied the Moon illusion with our unconscious inference of a flattened sky, and his explanation for the flattened shape seems promising.
The corona appeared golden yellow with a greenish tinge, and, thanks to the Moon illusion that works for objects near the horizon, it loomed unusually large against the twilight sky.
From Haidinger's brush to the Moon illusion, Out of the Blue introduces us to some of the most celebrated and bizarre atmospheric and optical effects visible to the naked eye.
The result," O'Meara continues, "was what I liken to the deep-sky version of the famed Moon illusion.
Countries near the center of the Earth's Moon-facing hemisphere will experience the eclipse practically overhead, while those along the rim will have the Moon very low in the sky, "magnified" by the well-known Moon illusion and perhaps nicely framed by distant landmarks.
Here's a small sample: iridescence in dewdrops, mirages, the red flash, black snow, the Moon illusion, imperfect images formed by the eye, freak reflections, illusions concerning rest and motion, pillars of light on roadways, a cat's eyes at night, reflection of light on mosses, scintillation from stones, and will-o'-the-wisps.
In his coverage of the thought-provoking theories concerning the Moon illusion, Minnaert fails to mention a most critical factor: the Moon's apparent diameter changes markedly between lunar perigee and apogee.