El sol de medianoche es un fenómeno natural observable en el norte del círculo polar ártico y al sur del círculo polar antártico, que consiste en que el Sol es visible las 24 horas del día, en las fechas próximas al solsticio de verano. El número de días al año con sol de medianoche es mayor, cuanto más cerca se esté del polo y es lo contrario a la noche polar.

Leer el artículo completo en Wikipedia · CC-BY-SA

The midnight sun is a natural phenomenon that occurs in the summer months in places north of the Arctic Circle or south of the Antarctic Circle, when the sun remains visible at the local midnight. Around the summer solstice (approximately 21 June in the Northern Hemisphere and 22 December in the Southern Hemisphere) the sun is visible for the full 24 hours, given fair weather. The number of days per year with potential midnight sun increases the farther towards either pole one goes. Although approximately defined by the polar circles, in practice the midnight sun can be seen as much as 55 miles (90 km) outside the polar circle, as described below, and the exact latitudes of the farthest reaches of midnight sun depend on topography and vary slightly year-to-year. There are no permanent, economically autonomous human settlements south of the Antarctic Circle, only research stations, so the countries and territories whose populations experience the midnight sun are limited to those crossed by the Arctic Circle: Canada (Yukon, Northwest Territories, and Nunavut), Greenland, Iceland, Finland, Norway, Russia, Sweden, and the United States (Alaska). A quarter of Finland's territory lies north of the Arctic Circle, and at the country's northernmost point the sun does not set at all for 60 days during summer. In Svalbard, Norway, the northernmost inhabited region of Europe, there is no sunset from approximately 19 April to 23 August. The extreme sites are the poles, where the sun can be continuously visible for half the year. The opposite phenomenon, polar night, occurs in winter, when the sun stays below the horizon throughout the day. Since the axial tilt of the Earth is considerable (approximately 23 degrees 27 minutes), the sun does not set at high latitudes in local summer. The duration of sunlight increases from one day during the summer solstice at the polar circle, to several weeks only 100 km closer to the pole, to six months at the poles. At extreme latitudes, the midnight sun is usually referred to as polar day. At the poles themselves, the sun rises and sets only once each year. During the six months that the sun is above the horizon, it spends the days continuously moving in circles around the observer, gradually spiralling higher and reaching its highest circuit of the sky at the summer solstice. Because of atmospheric refraction, and also because the sun is a disk rather than a point, the midnight sun may be experienced at latitudes slightly below the polar circle, though not exceeding one degree (depending on local conditions). For example, Iceland is known for its midnight sun, even though most of it (Grímsey is the exception) is slightly south of the Arctic Circle. For the same reasons, the period of sunlight at the poles is slightly longer than six months. Even the northern extremities of Scotland (and places at similar latitudes, such as St. Petersburg) experience twilight in the northern sky at around the summer solstice. Observers at heights appreciably above sea level can experience extended periods of midnight sun as a result of the "dip" of the horizon viewed from altitude.

Leer el artículo completo en Wikipedia · CC-BY-SA