Midnight sun
The
midnight sun is a
phenomenon occurring in
latitudes north of the
Arctic Circle and south of the
Antarctic Circle where the
sun is continuously visible for at least 24 hours once per year. 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, northern
Norway,
Sweden and
Finland, and extremities of
Russia such as
Novaya Zemlya and the cities of
Murmansk,
Norilsk and
Vorkuta. A quarter of
Finland's territory lies above the
Arctic Circle, and as a consequence the midnight sun can be experienced — for more and more days, the further north one goes. At Finland's northernmost point, the sun does not set for 73 days during summer. At
Nordkapp in
Norway, what is normally denoted as the northermost point in Europe, there are 76 days (from 14. May to 30. July) of proper midnight sun and an additional few days with partial sun before and after.
The opposite phenomenon,
polar night, 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
summer solstice at the
polar circle to approximately 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 Circle and Antarctic Circle to 186 days at the
poles.
At the poles themselves, the sun only rises once and sets once, each year. The sun spends those days constantly moving around the horizon, reaching its highest circuit of the sky at the summer solstice.
Due to refraction, the midnight sun may be experienced at latitudes slightly below the polar circle, though not exceeding one degree (depending on local conditions). For example, it is possible to experience the midnight sun in Iceland, even though most of it (
Grímsey being a notable exception) is slightly south of the Arctic Circle.
*
Video • Norway • Bodø/MjelleLocations above 60 degrees latitude that are south of the Arctic Circle or north of the Antarctic Circle experience midnight
twilight instead. The sun is just below the horizon, so that daytime activities, such as reading, are still possible without resorting to artificial light.
White nights have become a common symbol of
Saint Petersburg,
Russia, where they occur from about
11 June to
11 July, and the last 10 days of June are celebrated with cultural events.
Scandinavia and
Alaska, where this effect can also be observed, are both known as
The Land of the Midnight Sun.
Many find it difficult to fall asleep during the night when the sun is shining. In general, visitors and newcomers are most affected; they are easily spotted in residential areas by the aluminum folium glued onto their bedroom windows to obtain darkness inside. Some natives are also affected, but in general to a lesser degree. The effect of the
polar night, that is, not experiencing day for long durations of time, can be extreme fatigue. High intensive daylight coloured lamps are popular to ease the problem.
The movie
Insomnia tells the story of a fictional police detective in Norway who suffers from insomnia due to, among other things, the midnight sun. A
2002 remake of the film is set in Alaska.
The Midnight Sun is also the title of a
Twilight Zone episode.
Most of the plot of the movie
White nights takes place during a midnight sun period in Siberia.
