The polar night occurs when the night lasts for more than 24 hours. This occurs only inside the polar circles. The opposite phenomenon, the polar day, or midnight Sun, occurs when the Sun stays above the horizon for more than 24 hours. “Night” is understood as the center of the Sun being below a free horizon. Since the atmosphere bends the rays of the Sun, “light wins over darkness” by a few degrees. Hence the area that is affected by polar night is somewhat smaller than the area of midnight Sun. The polar circle is located at a latitude between these two areas, at the latitude of approx. 66.5 degrees. For instance, in the most northern city of Sweden, Kiruna (located at the northern latitude of 67°51′), the polar night lasts for around 28 twenty-four hour periods, while the midnight Sun lasts around 50 twenty-four hour periods.