Why the moon big?

Why the moon big?

Moon illusion (illusion of the Moon) - an optical illusion which creates the impression that the perceived size of the moon increases several times, when the Earth's moon is above the horizon, and decrease when the Moon soars high into the sky.The projection of a celestial object on the retina of our eye remains unchanged in both cases.The interest of humanity to the mysterious phenomenon known since ancient times, which was reflected in many of the testimonies of antiquity.In the end, every curious child asked where large moon, answer with certainty: in the land!So why are all the same, down to the horizon, the moon became more?

Theory

popular misconception explains the increase in the size of celestial bodies at the horizon so-called effect of increasing, the cause of which supposedly lies in the Earth's atmosphere.In fact, astronomical refraction factor near the horizon on the contrary, slightly reduces the size of the observed slightly priplyuschivaya moon on its vertical axis.The angular size of the celestial object depends solely on the distance between it and the observer.Small changes in this distance in no way connected with the optical sensation caused by an error of perception, when the Moon is near the horizon seems to be repeatedly extended.Measurements show that the angular size of our satellite vary by no more than 0,5 °.The size of the projection on the retina is 0.15mm.

Practice

The easiest way to prove the illusory nature of the increase of the moon - is to compare its size with the size of elongated coin in his hand, covering one eye.Comparing the size of a coin, where "the biggest" The moon is visible above the horizon, and repeating the experience when the night light will rise to the zenith, it is easy to make sure that its size does not change.light Size can be determined either by setting its physical parameters, or through the angular size of the object.Differences between the two due to the peculiarities of our sight.For example, if two identical objects placed one in five, and the other ten meters from the observer, their actual dimensions will vary angled twice.The observer also did not confirm.Conversely, if the angular size of a distant object is equal to the angular size of a close observer would argue that an object approaches twice the distance.

Conclusion

Why the moon big?To date, no consensus on the nature of the known optical effect is not present.The debate revolves around the question: Moon near the horizon is increased due to the fact that it seems to be an increased perceived angular size or physical?In other words, we see the Moon as it approached us, or increase in size?The final explanation is still waiting for its researchers.