Why is the moon big?
Moon illusion (the illusion of the moon) is an optical illusiona deception giving the impression that the perceived dimensions of the moon increase several times when the Earth's satellite is above the horizon, and decrease when the moon soars high into the sky. The projection of the heavenly body on the retina of our eye remains unchanged in both cases. The interest of mankind in the mysterious phenomenon is known from ancient times, which is reflected in many evidences of antiquity. In the end, every curious child on the question, where the big Moon, with confidence will answer: at the ground! So why, after all, having fallen to the horizon line, the Moon has become larger?
A popular misconception explains the increasethe dimensions of celestial bodies near the horizon by the so-called magnification effect, the cause of which is allegedly hidden in the Earth's atmosphere. In fact, the factor of astronomical refraction near the horizon on the contrary, somewhat reduces the observed dimensions, slightly flattening the moon along its vertical axis. The angular dimension of a celestial object depends solely on the distance between it and the observer. Small changes in this distance are in no way related to the optical sensation caused by the perception error, when the Moon at the horizon seems to be multiplied. The measurements show that the angular dimensions of our satellite vary by no more than 0.5 °. The size of the projection on the retina is 0.15 mm.
The simplest way to prove illusionincreasing the moon - it's to compare its size with the size of a coin stretched in the hand, covering one eye. Comparing the size of the coin, when the "largest" Moon is visible above the horizon, and repeating the experiment, when the night star rises to the zenith, it is easy to make sure that its size does not change. The size of the light can be determined either by setting its physical parameters, or through the angular size of the object. The differences between these two concepts are due to the peculiarity of our vision. For example, if two identical objects are placed one in five and the other in ten meters from the observer, then their real angular dimensions will differ by a factor of two. The observer does not confirm this. Conversely, if the angular size of the distant object is equal to the angular size of the closer one, the observer will begin to assert that the approximate object is twice as long as the remote object.
Why is the moon big? To date, there is no consensus on the nature of the known optical effect. The discussion is centered around the question: Does the moon at the horizon increase due to the fact that its perceived angular size or physical size seems to be enlarged? In other words: do we see the moon as if approximate to us or enlarged in size? The final explanation is still waiting for its researcher.