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| | Night is a time interval, during which, for a certain location on surface of celestial body (planet, its satellite, etc.), the central shining (Sun, stars) is below the horizon line.
Duration of night period for a certain location depends on its latitude, axial tilt of planet with respect to plane of its orbit and angle, formed by axis of rotation and direction on central shining. Day and night sides of celestial bodies are divided by terminator.
Since rotation axes of planets of Solar system are not perpendicular with respect to planes of their orbits, duration of nights on planets change during their revolution round the Sun with annual periodicity. Identical duration of day and night is observed during equinoxes, when the Earth axis (or rotation axis of heavenly body) is perpendicular to ecliptic; during solstices, the difference between the duration of day and night is maximum, when axis of the Earth has maximum inclination with respect to ecliptic.
Within polar circles of planets, duration of night can exceed solar days (polar night). Polar night lasts from one day at latitude of polar circle and up to six months on pole. |
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Past Saturday at 8pm (local time) millions of people across the world as well as thousands of businesses turned off their lights for an hour to promote electricity conservation. The event is called
