The most remote point or distance to which the human eye is able to focus is at infinity, where in theory our sight would reach. However, assuming a visual field without accidents that impede vision, the curvature of the Earth limits the distance above the horizon that we can reach visually. This distance is about 40 kilometers .
Sometimes, however, it is possible to see objects behind the horizon. The reason: the refraction of light, a phenomenon that occurs when light passes through layers of air at different temperatures and, therefore, at different densities. This causes that, for example, at the moment of sunset in which we see it as a large red ball, the star is actually below the horizon.
