Midnight sun

The midnight sun at Nordkapp, Norway.

The Alta Fjord in Alta, Norway bathed in the Midnight Sun.

Midnight sun in Kiruna, Sweden.

The midnight sun is a natural phenomenon occurring in summer months at places north of the Arctic Circle and south of the Antarctic Circle where the sun remains visible at the local midnight. Around the solstice (June 21 in the north and December 21 in the south) and given fair weather the sun is visible for the full 24 hours. 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 midnight sun can be seen as much as 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 human settlements south of the Antarctic Circle, so the countries and territories whose populations experience it are limited to the ones crossed by the Arctic Circle, e.g. Canada (Yukon, Northwest Territories, and Nunavut), Denmark (Greenland), Finland, Sápmi, Norway, Russia, Sweden, the United States (Alaska), and extremities of Iceland. 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 a half 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 a hundred kilometres closer to the pole, to six months at the poles. At extreme latitudes, it is usually referred to as polar day.

At the poles themselves, the sun only rises once and sets once each year. During the six months when 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.

Due to 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, 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. The same mechanisms cause the period of sunlight at the poles to last slightly more than six months. Even the northern extremities of Scotland (and those places on similar latitudes such as St. Petersburg) experience a permanent twilight in the northern sky at these times.

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.

Time zones and daylight saving time

For purposes of this article, the term "midnight sun" refers to the phenomena of 24 consecutive hours of sunlight north of the Arctic Circle or south of the Antarctic Circle. There are, however, some instances which are sometimes referred to as "midnight sun", even though they are in reality due to meandering time zones and the observance of daylight saving time. For instance, in Fairbanks, Alaska, which is located south of the Arctic Circle, the sun sets at 12:47 a.m. on the summer solstice. This is because Fairbanks is one hour ahead of its idealized time zone (due to meandering for the purpose of keeping most of the state on one time zone) and because the state of Alaska observes daylight saving time. This means that solar culmination occurs at roughly 2 p.m. instead of at 12 noon, as in most places.

If a precise moment for the genuine "midnight sun" is required, the observer's longitude, the local civil time and the equation of time must be taken into account. The moment of the sun's closest approach to the horizon coincides with its passing due north at the observer's position, which occurs only approximately at midnight in general. Each degree of longitude east of the Greenwich meridian makes the vital moment exactly 4 minutes earlier than midnight as shown on the clock, while each hour that the local civil time is ahead of coordinated universal time (also known as GMT) makes the moment an hour later. These two effects must be added. In addition the equation of time (which depends on the date) must be added: a positive value on a given date means that the sun is running slightly ahead of its average position, so the value must be subtracted.^[1]

As an example, at the North Cape at midnight on June 21/22, the east longitude of 25.9 degrees makes the moment 103.2 minutes earlier by clock time; but the local time, 2 hours ahead of GMT, takes it 120 minutes later by clock time. The equation of time at that date is -2.0 minutes. So the sun's lowest elevation occurs 120 - 103.2 + 2.0 minutes after midnight, i.e. at 00.19. On other nearby dates the only thing different is the equation of time, so this remains a reasonable estimate for a considerable period. The sun's altitude remains within half a degree of the minimum of about 5 degrees for about 45 minutes either side of this time.

White Nights

Locations where the sun is less than 6 (or 7^[2]) degrees below the horizon which are above 60° 34’ (or 59° 34’) latitude that are south of the Arctic Circle or north of the Antarctic Circle experience midnight twilight instead. So that daytime activities, such as reading, are still possible without artificial light on a clear night.

White Nights have become a common symbol of Saint Petersburg, Russia, where they occur from about June 11 to July 2,^[2] and the last 10 days of June are celebrated with cultural events known as the White Nights Festival.

When to see the midnight sun

Map showing the dates of midnight sun at various latitudes (left) and the total number of nights.

The Midnight Sun is visible at the Arctic Circle from June 12 until July 1. The further north one goes the longer this period extends.

At North Cape, Norway, known as the northernmost point of Continental Europe this period extends approximately from May 14 to July 29. On the Svalbard archipelago further north this period extends from April 20 to August 22.^[3]

Effect on people

Many find it difficult to fall asleep during the night when the sun is shining. In general, visitors and newcomers are most affected. Some natives are also affected, but in general to a lesser degree. The effect of the midnight sun, that is, not experiencing night for long durations of time, is said to cause hypomania, which is characterized by persistent and pervasive elevated or irritable mood.

The midnight sun also poses special challenges to religious people such as Jewish people who have religious rites based around the 24 hour day/night cycle. In the Jewish community this has given rise to a body of Jewish law in the polar regions, which attempts to deal with the special challenges of adhering to the Mitzvah in such conditions. Another related religion that suffers from this is Islam, where fasting during daylight hours in Ramadan would imply total abstinence. Also, Muslims have 5 obligatory prayers daily which are timed according to position of the sun, so it becomes difficult for them to decide the prayer times; however, they can follow the timings of the closest place that has a normal sun cycle or the timings of Mecca, the holiest city of Islam. The Seventh Day Adventists and other Sabbath-keeping Christians keep the Sabbath day holy when the sun goes down Friday, until the sun goes down Saturday, and Joseph Bates suggested to keep the equatorial sunset as a reference to the Sabbath time, for those that deal with the midnight sun because the equator sunrise and sunset occur consistently throughout the year plus or minus 10 minutes at 6 a.m. and 6 p.m. respectively.^[4]

In fiction

In the film Insomnia and its American remake, the protagonist suffers from insomnia partially brought on by the midnight sun while investigating a murder north of the Arctic Circle (Norway in the original, and Alaska in the remake).
In "The Midnight Sun", an episode of The Twilight Zone, the Earth is on a collision course with the sun, causing a midnight sun effect.
The episode of Northern Exposure entitled Midnight Sun explores the effects of the phenomenon on the small Alaskan town's residents.
In the Stephen Sondheim musical 'A Little Night Music', the two Night Waltzes deal specifically with the phenomenon of Midnight Sun.

References

^ H. Spencer Jones, General Astronomy (Edward Arnold, London, 1922), Chapters I-III
^ ^a ^b Great Soviet Encyclopedia
^ Trygve B. Haugan, ed. Det Nordlige Norge Fra Trondheim Til Midnattssolens Land (Trondheim: Reisetrafikkforeningen for Trondheim og Trøndelag. 1940)
^

Additional Reading

1. Lutgens F.K., Tarbuck E.J. (2007) The Atmosphere, Tenth Edition, page 39, PEARSON, Prentice Hall, NJ.

External links

Parts of a day

	Dawn–Twilight–Sunrise Morning Daylight Evening Sunset–Twilight–Dusk Night

	Related articles: Blue hour Golden hour Terminator Forenoon Noon Afternoon Midnight Daytime Midnight sun

This article is copied from an article on Wikipedia® - the free encyclopedia created and edited by its online user community. The text was not checked or edited by anyone on our staff. Although the vast majority of Wikipedia® encyclopedia articles provide accurate and timely information, please do not assume the accuracy of any particular article. This article is distributed under the terms of GNU Free Documentation License.