Another common illusion of physical origin is astronomical refraction, which consists in the deviation of the visible electromagnetic spectrum, coming from outside Earth’s atmosphere, by layers of air of different density. This deformation consists of an increase in the declination of celestial bodies on the celestial vault, that is, a raising of the object with respect to its real position in space. This means that refraction delays the time of the setting of celestial bodies and anticipates their rising. This type of optical illusion is obviously zero at the zenith and maximum at the horizon. Let us now see some values of astronomical refraction:
A common experience is to read the sunset times in the ephemerides, but when you observe them you can notice that in fact there are delays in the instant when the Sun touches the horizon compared to the ephemerides. These delays are due precisely to refraction.
Shift of Venus at sunset; in this case atmospheric refraction is also present, which has generated a mirage
