Midnight sun
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Midnight sun, also known as polar day, is a
The opposite phenomenon, polar night, occurs in winter, when the Sun stays below the horizon throughout the day.
Geography
Because there are no permanent human settlements south of the Antarctic Circle, apart from research stations, the countries and territories whose populations experience midnight sun are limited to those crossed by the Arctic Circle: Canada (Yukon, Nunavut, and Northwest Territories), Finland, Greenland, Iceland, Norway, Russia, Sweden, and the United States (state of Alaska).
The largest city in the world north of the Arctic Circle, Murmansk, Russia, experiences midnight sun from 22 May to 22 July (62 days).
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 72 days during summer.[1]
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 North Pole has midnight sun for about 6 months, from approximately 18 March to 24 September.[2] South Pole, Antarctica has midnight sun and experiences this from approximately 20 September to 23 March (about 6 months).[3]
Polar circle proximity
Because of atmospheric refraction, and also because the Sun is a disc rather than a point in the sky, midnight sun may be experienced at latitudes slightly south of the Arctic Circle or north of the Antarctic 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 the United Kingdom (and places at similar latitudes, such as Saint Petersburg) experience twilight throughout the night in the northern sky at around the summer solstice.
Places sufficiently close to the poles, such as
White nights
Locations where the Sun remains less than 6 (or 7[4]) degrees below the horizon – between about 60° 34’ (or 59° 34’) latitude and the polar circle – experience midnight twilight[5] instead of midnight sun, so that daytime activities, such as reading, are still possible without artificial light on a clear night. This happens in both Northern Hemisphere summer solstice and Southern Hemisphere summer solstice. The lowest latitude to experience midnight sun without a golden hour is about 72°34′ North or South.
Month | Lowest latitude to experience white night |
Lowest latitude to experience midnight sun |
Highest latitude to experience 100% darkness |
---|---|---|---|
January | 59º 54' S | 66º 04' S | 48º 54' S |
February | 64º 47' S | 70º 57' S | 53º 47' S |
March (before equinox) |
74º 47' S | 80º 57' S | 63º 47' S |
March (after equinox) |
78º 45' N | 84º 55' N | 67º 45' N |
April | 68º 09' N | 74º 19' N | 57º 09' N |
May | 61º 03' N | 67º 13' N | 50º 03' N |
June | 59º 34' N | 65º 44' N | 48º 34' N |
July | 59º 54' N | 66º 04' N | 48º 54' N |
August | 65º 02' N | 71º 12' N | 54º 02' N |
September (before equinox) |
74º 47' N | 80º 57' N | 63º 47' N |
September (after equinox) |
78º 45' S | 84º 55' S | 67º 45' S |
October | 68º 19' S | 74º 19' S | 57º 09' S |
November | 61º 03' S | 67º 13' S | 50º 03' S |
December | 59º 34' S | 65º 44' S | 48º 34' S |
White Nights have become a common symbol of Saint Petersburg, Russia, where they occur from about 11 June to 1 July,[4] and the last 10 days of June are celebrated with cultural events known as the White Nights Festival.
The northernmost tip of Antarctica also experiences white nights near the Southern Hemisphere summer solstice.
Explanation
Since the axial tilt of Earth is considerable (23 degrees, 26 minutes, 21.41196 seconds), at high latitudes the Sun does not set in summer;[6] rather, it remains continuously visible for one day during the summer solstice at the polar circle, for several weeks only 100 km (62 mi) closer to the pole, and for six months at the pole. At extreme latitudes, midnight sun is usually referred to as polar day.
At the poles themselves, the Sun rises and sets only once each year on the equinox. During the six months that the Sun is above the horizon, it spends the days appearing to continuously move in circles around the observer, gradually spiralling higher and reaching its highest circuit of the sky at the summer solstice.
Time zones and daylight saving time
The term "midnight sun" refers to the consecutive 24-hour periods of sunlight experienced north of the Arctic Circle and south of the Antarctic Circle. Other phenomena are sometimes referred to as "midnight sun", but they are caused by
If a precise moment for the genuine "midnight sun" is required, the observer's
As an example, at the
When it rotates on its own axis, it sometimes moves closer to the Sun. During this period of Earth's rotation from May to July, Earth tilts at an angle of 23.5 degrees above its own axis in its orbit. This causes the part of Norway located in the Arctic region at the North Pole of Earth to move very close to the Sun and during this time the length of the day increases. It can be said that it almost never subsides. Night falls in Norway's Hammerfest at this particular time of year.
Duration
The number of days per year with potential midnight sun increases the closer one goes toward either pole. Although approximately defined by the polar circles, in practice, midnight sun can be seen as much as 90 km (56 mi) outside the polar circle, as described below, and the exact latitudes of the farthest reaches of midnight sun depend on topography and vary slightly from year to year.
Even though at the Arctic Circle the center of the Sun is, per definition and without refraction by the atmosphere, only visible during one summer night, some part of midnight sun is visible at the Arctic Circle from approximately 12 June until 1 July. This period extends as one travels north: At Cape Nordkinn, Norway, the northernmost point of Continental Europe, midnight sun lasts approximately from 14 May to 29 July. On the Svalbard archipelago farther north, it lasts from 20 April to 22 August.[8]
Southern and Northern poles
Also, the periods of polar day and polar night are unequal in both polar regions because the Earth is at
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.
References
- ^ Nuorgam, Lapland, Finland — Sunrise, Sunset, and Daylength, May 2022
- ^ "Time and Date.com - North Pole". Time and Date.com. Retrieved March 12, 2024.
- ^ "Time and Date.com - South Pole, Antarctica". Time and Date.com. Retrieved March 12, 2024.
- ^ a b Great Soviet Encyclopedia
- ^ "Sunrise and sunset times in Saint-Petersburg". www.timeanddate.com. Retrieved 2023-08-26.
- ^ "What is the Midnight Sun Phenomenon? | Earth Phenomena | Planetary Science". Scribd. Retrieved 2017-08-25.
- ^ H. Spencer Jones, General Astronomy (Edward Arnold, London, 1922), Chapters I-III
- ^ Trygve B. Haugan, ed. Det Nordlige Norge Fra Trondheim Til Midnattssolens Land (Trondheim: Reisetrafikkforeningen for Trondheim og Trøndelag. 1940)
Further reading
- Lutgens F.K., Tarbuck E.J. (2007) The Atmosphere, Tenth Edition, page 39, PEARSON, Prentice Hall, NJ.