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The midnight sun is a phenomenon , occurring in latitudes north of the arctic circle and south of the antarctic circle, where the sun is visible during at least 24 hours. Since there are no permanent human settlements south of the antarctic circle, the countries and territories whose population experiences it are limited to Alaska, northern Canada, Greenland, Iceland (due to refraction, northern Norway, Sweden and Finland, and extremities of Russia such as Novaya Zemlya or Murmansk.

The opposite phenomenon, polar nightThe polar night is the night lasting more than 24 hours, usually inside the polar circles. Various kinds of polar night exist. A common misunderstanding is that at each point inside the polar circle, or each place where midnight sun occurs, the shortest d, is observed in winter when the sun is sufficiently below the horizon, so that there is insufficient sunlight or no light at all. (A lingering dusk may occur, if the sun is only 12 degrees or less below the horizon.)

Since the earth's axis is tilted with respect to the ecliptic by approximately 23 degrees 26 minutes (commonly rounded to 23 degrees and a half), the sun does not set at high latitudes in (local) summer. The duration of the midnight sun increases from one day during the summerSummer is one of the four temperate seasons. Astronomically, it begins with the summer solstice (around 21 June in the Northern hemisphere, and 21 December in the Southern hemisphere) and ends with the autumn equinox (around 21 September in the Northern h solsticeSolstice is an astronomical term regarding the position of the Sun in relation to the celestial equator. It is related to the axial tilt of the planet, and not the Solar apsides ( aphelion and perihelion) of the planet, as many people commonly believe. at the polar circle to approximately <-- because of refraction --> six months at the poles. At extreme latitudes, it is usually referred to as polar day. The length of the time when the sun is above the horizon varies from 20 hours at the Arctic CircleThe Arctic Circle is one of the five major circles of latitude that mark maps of the Earth. This is the parallel of latitude that runs 66° 33' 38" north of the Equator. Everything north of this circle is known as the Arctic, and the zone just to the south and Antarctic CircleThe Antarctic Circle is one of the five major circles of latitude that mark maps of the Earth. It is the parallel of latitude 66° 33' 38" south of the equator. Everywhere within the Antarctic Circle there is at least one day of the year for which the Sun to 186 days at the Poles.

Due to refraction, the midnight sun may be experienced at latitudes slightly below the polar circle, though not exceeding a degree (depending on local conditions). For example, it is possible to experience the midnight sun in Iceland, even though it is slightly south of the arctic circle.

Locations at latitudes up to 60 degrees experience midnight twilightTwilight is the time before sunrise and after sunset when sunlight reflected from particles in the upper atmosphere illuminates the lower atmosphere and the surface of the earth. Civil twilight is the time when the sun is below the horizon, but when no st instead. The sun is just below the horizon, so that daytime activities, such as reading, are still possible without resorting to artificial light. These are the white nightWhite night is a night on which it is never getting completely dark, because the sun does not descend sufficiently far below the horizon. It happens in high latitudes in summer. White nights have became a common symbol of St. Petersburg, Russia. Natural ps experienced, for example, in St. Petersburg, Russia from about 11 June to 11 July.