Night or nighttime (also spelled night-time or night time) is the period of ambient darkness from sunset to sunrise during each 24-hour day, when the Sun is below the horizon. The exact time when night begins and ends (equally true with evening) depends on the location and varies throughout the year. When night is considered as a period that follows evening, it is usually considered to start around 8 pm and to last to about 4 am. Night ends with coming of morning at sunrise.The word can be used in a different sense as the time between bedtime and morning. 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. For example: "It was nice to see you. Good night!" Unlike "good morning", "good afternoon", and "good evening", "good night" (or "goodnight") is not used as a greeting.
Complete darkness or astronomical 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. 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.
The opposite of night is day (or "daytime", to distinguish it from "day" referring to a 24-hour period).