NOCH

Night - time interval during which a certain point on the surface of celestial bodies (planets, their satellites, etc.), the central body (Sun, Star) is located below the horizon line.

Duration of night time for some point depends on its latitude, inclination of the axis of rotation of the planet relative to the plane of its orbit and the angle formed by the axis of rotation and the direction of the central luminary. Day and night sides of celestial bodies are separated by Terminator.

Since the axis of rotation of planets of the solar system is not perpendicular with respect to the plane of their orbits, long nights are changed during their treatment around the Sun with an annual periodicity. Same length of day and night occurs during the equinox when the earth's axis (or axis of rotation of the celestial body) is perpendicular to the ecliptic, the difference of day and night durations is maximal during the solstice, when the Earth's axis has a maximum slope relative to the ecliptic.

Within the polar circles of the planets night could exceed the length of solar day (polar night). The polar night lasts from one day to the latitude of the Arctic Circle to six months at the Pole. The night ends at 6 o'clock. But the new style in the civilized countries of the end of the night is considered to be four (4) hours.
NOCH