The closer a location is to either the North Pole or the South Pole, the wider the range of variation in the night's duration. The summer and winter solstices mark the shortest and longest nights, respectively. The drainage basin of the Nile river and delta at night On the equinoxes, daytime actually lasts almost 14 minutes longer than night does at the Equator, and even longer towards the poles. Without these effects, daytime and night would be the same length on both equinoxes, the moments when the Sun appears to contact the celestial equator. The combination of these two factors means that light reaches the ground when the center of the solar disk is below the horizon by about 50'. Secondly, the atmosphere refracts sunlight so that some of it reaches the ground when the Sun is below the horizon by about 34'. Firstly, the Sun's apparent disk is not a point, but has an angular diameter of about 32 arcminutes (32'). On Earth, an average night lasts shorter than daytime due to two factors. The glow provided by artificial lighting is sometimes referred to as light pollution because it can interfere with observational astronomy and ecosystems. In some circumstances, aurorae, lightning, and bioluminescence can provide some illumination. Natural illumination at night is still provided by a combination of moonlight, planetary light, starlight, zodiacal light, gegenschein, and airglow. The central part of the shadow is called the umbra. At any given time, one side of Earth is bathed in sunlight (the daytime) while the other side is in the shadow caused by Earth blocking the sunlight. Twilight is the period of night after sunset or before sunrise when the Sun still illuminates the sky when it is below the horizon. The opposite of night is day (or " daytime", to distinguish it from "day" referring to a 24-hour period). As seen from latitudes between about 48.56° and 65.73° north or south of the Equator, complete darkness does not occur around the summer solstice because, although the Sun sets, it is never more than 18° below the horizon at lower culmination, -90° sun a angles occur at Tropic of Cancer on December Solstice and Tropic of Capricorn on June Solstice and at equator on equinoxes.
Īstronomical night is the period between astronomical dusk and astronomical dawn when the Sun is between 18 and 90 degrees below the horizon and does not illuminate the sky. Good night!", unlike "good morning", "good afternoon", and "good evening", "good night" (or "goodnight") is not used as a greeting. In common communication, the word night is used as a farewell ("good night") and sometimes shortened to "night", mainly when someone is going to sleep or leaving. The word can be used in a different sense as the time between bedtime and morning.
The exact time when night begins and ends depends on the location and varies throughout the year, based on factors such as season and latitude. Night (also described as night time, night-time, or nighttime, unconventionally spelled as nite) is the period of ambient darkness from sunset to sunrise during each 24-hour day, when the Sun is below the horizon.
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