Monday, January 21, 2013

Why the Moon looms large on the horizon: Binocular disparity as an explanation for the moon illusion

Is the Moon really larger at the horizon than overhead, or is this an illusion, created in our heads? [Photograph by Robert Arn, AstroArn Photography].
Joseph Antonides, Toshiro Kubota

We present another explanation for the moon illusion, in which the moon looks larger near the horizon than near the zenith. In our model, the sky is considered a spatially contiguous and geometrically smooth surface. When an object (like the moon) breaks the contiguity of the surface, humans perceive an occlusion of the surface rather than an object appearing through a hole. Binocular vision dictates that the moon is distant, but this perception model dictates that the moon is closer than the sky. To solve the dilemma, the brain distorts the projections of the moon to increase the binocular disparity, which results in increase of the angular size of the moon. The degree of the distortion depends upon the apparent distance to the sky, which is influenced by the surrounding objects and the condition of the sky. The closer the sky appears, the stronger the illusion. At the zenith, few distance cues are present, causing difficulty with distance estimation and weakening the illusion.

Read the research paper, HERE.

News story with commentary from MIT: "Moon illusion: New theory reignites debate over why Moon appears larger near the horizon," The Physics arXiv Blog, January 17, 2013

Full Moon rises over the ruins of the Temple of Poseidon, Cape Sounion, 69 km south-southeast of Athens, southernmost tip of the Attica peninsula in Greece. Seventeen sequential images by John Doukoumopoulos, June 18, 2008 [Lunar Picture of the Day (LPOD), June 20, 2008].

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