Life of people of Earth cannot be presented without the Moon. The night star not only inspires poets, it made possible origin and preservation of life on Earth. At all times the Moon raised a set of questions for the person.
Some mysteries of the Moon still wait for the solution. Scientists offer different hypotheses, but any does not explain everything. One of such riddles – the phenomenon known as "illusion of the Moon".
Illusion of the Moon
This phenomenon can observe everyone, and the telescope, rather clear sky is for this purpose not necessary. If to look at a night star during its rising or calling i.e. when the Moon is visible low over the line of the horizon, and then to look at it in a zenith, it is easy to notice that diameter of a lunar disk changes. Low over the horizon it looks several times more, than highly in the sky.
Certainly, the size of the Moon cannot change, only how it looks from the point of view of the terrestrial observer changes.
How to explain
Attempts to explain this phenomenon were made in Ancient Greece. Then the idea was introduced that in illusion the atmosphere of Earth is guilty, but modern scientists do not agree with it. Beams of heavenly bodies really refract in the atmosphere, but the visible size of the Moon at the horizon because of it does not increase, and decreases. The solution of "increase" and "reduction" of Lugy should be looked for not so much in the physical phenomena how many in features of human visual perception. It is possible to prove it by means of the simplest experience: if to close one eye and to look at some small subject (for example, a coin) against the background of a "big" lunar disk over the horizon, and then – against the background of the "small" Moon in a zenith it will turn out that the ratio of the sizes of a disk and this subject did not change. One of hypotheses connects "increase" in a lunar disk with comparison it with terrestrial reference points. It is known that the it is more than a distance from the observer to an object, the less projection of an object to a retina, the "less" it from the point of view of the observer. But the konstantnost – constancy of the perceived size of objects is peculiar to visual perception. The remote object of people sees as remote, but not small. The lunar disk which is low over the line of the horizon is located "behind" houses, trees and other objects which are seen by the person, and is perceived as more remote. In terms of a perception konstantnost it is distortion of the perceived size which has to be compensated, and the "remote" Moon becomes "big". When the Moon is visible in a zenith, its size could not be compared therefore illusion of increase does not arise. Other hypothesis explains this phenomenon with divergence (divergence) and convergence (data) of eyes. Looking at the Moon in a zenith, the person throws back the head that causes divergence of eyes which should be compensated by convergence. Convergence in itself is connected with observation of the objects which are brought closer to the observer therefore the Moon in a zenith is perceived as closer object, than on the horizon. At preservation of the size of a disk "closer" means "smaller". However, it is impossible to call any of these hypotheses faultless. Illusion of the Moon waits for the solution.