Some secrets of the moon still await the explanation.Scientists propose different hypotheses, but none explains all.One of these mysteries - a phenomenon known as the "moon illusion."

Moon Illusion

This phenomenon can watch each and it does not need a telescope sufficiently clear sky.If you look at the night light during sunrise or sunset, ie,at a time when the moon is visible low on the horizon, and then look at it at its zenith, it is easy to notice that the diameter of the lunar disk changes.Low on the horizon, it appears several times more than in the sky.

Of course, the sheer size of the moon can not change, only change the way it looks from the perspective of an observer on earth.

How to explain

Attempts to explain this phenomenon date back to ancient Greece.It was th
en suggested that the illusion blame the Earth's atmosphere, but modern scholars disagree.The rays of the heavenly bodies really are refracted in the atmosphere, but the apparent size of the Moon near the horizon because of this does not increase but decreases.

unraveling "increase" and "reduce" Lugy be sought not so much in the physical phenomena as the peculiarities of human visual perception.Prove it, you can use simple experiment: if you close one eye and look at any small object (eg a coin) on the background of the "big" of the lunar disk above the horizon, and then - on the background of the "little" of the moon at the zenith would be that the ratiodisk size and the subject has changed.

One hypothesis links the "increase" of the lunar disk to its comparison with earthly landmarks.It is known that the greater the distance from the observer to the object, the smaller the projection of the object on the retina, the "less than" he observer's viewpoint.But visual perception is peculiar constancy - constancy of the perceived size of the object.Remote object person sees it as a distant, not small.

lunar disk that is low on the horizon, is located "behind" the houses, trees and other objects that people see, and is perceived as more distant.From the standpoint of perceptual constancy of this distortion is perceived size, which must be compensated, and "remote" moon becomes "large".When the moon is visible at the zenith of its size have nothing to compare, so there is no increase in illusion.

Another hypothesis explains this phenomenon divergence (divergence) and convergence (data) eyes.Looking at the moon at its zenith, a man throws his head back, causing the divergence of the eye that has to compensate for the convergence.By itself, the convergence associated with the supervision of the observer close to the object, so the moon at the zenith is perceived as an object closer than the horizon.When you save a disc size "closer" means "less."

However, none of these hypotheses can not be called perfect.Moon Illusion is waiting for his clues.