Nights are shorter than days on average due to two factors. One, the sun is not a point, but has an apparent size of about 32 minutes of arcarcminutes. Two, the atmosphere refracts sunlight so that some of it reaches the ground when the sun is below the horizon by about 34 minutes of arcarcminutes. The combination of these two factors means that light reaches the ground when the centre of the sun is below the horizon by about 50 minutes of arcarcminutes. Without these effects, day and night would be the same length at the [[Autumnal equinox|autumnal]] (autumn/fall) and [[Vernal equinox|vernal]] (spring) [[equinox]]es, the moments when the sun passes over the [[equator]]. In reality, around the equinoxes the day is almost 14 minutes longer than the night at the equator, and even more towards the [[geographical pole|pole]]s. The summer and winter [[solstice]]s mark the shortest and the longest night, respectively. The closer a location is to either the [[North Pole]] or the [[South Pole]], the larger the range of variation in the night's length. Although equinoxes occur with a day and night close to equal length, before and after an equinox the ratio of night to day changes more rapidly in [[high latitude]] locations than in [[low latitude]] locations. In the [[Northern Hemisphere]], [[Denmark]] has shorter nights in June than [[India]] has. In the [[Southern Hemisphere]], [[Antarctica]] has longer nights in June than [[Chile]] has. The Northern and Southern Hemispheres of the world experience the same patterns of night length at the same latitudes, but the cycles are 6 months apart so that one hemisphere experiences long nights (winter) while the other is experiencing short nights (summer).
Between the pole and the polar circle, the variation in daylight hours is so extreme that for a portion of the summer, there is no longer an intervening night between consecutive days and in the winter there is a period that there is no intervening day between consecutive nights.
