People have long noted that a full moon seems to shrink and expand in size depending on its heavenly position. A moon looks larger near the horizon than perched high in the sky, although its distance from Earth remains the same.
Scientists have yet to unravel the so-called moon illusion. Experiments now indicate that a horizon moon grows larger because it lies near visual markers of depth and distance on Earth's landscape that make it look much farther away than a higher moon.
Psychologist Lloyd Kaufman of Long Island University in Brookville, N.Y., and his son, physicist James H. Kaufman of the IBM Almaden Research Center in San Jose, Calif., conducted the new research.
"Our results leave no doubt that perceived-distance information plays a primary role in creating the moon illusion," Lloyd Kaufman says.
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