Midnight sun, also known as polar day, is a natural phenomenon that occurs in the summer months in places north of the

Arctic Circle The Arctic Circle is one of the two polar circles, and the northernmost of the five major circle of latitude, circles of latitude as shown on maps of Earth at about 66° 34' N. Its southern counterpart is the Antarctic Circle. The Arctic Circl ...

or south of the Antarctic Circle, when the Sun remains visible at the local midnight. When midnight sun is seen in the

Arctic The Arctic (; . ) is the polar regions of Earth, polar region of Earth that surrounds the North Pole, lying within the Arctic Circle. The Arctic region, from the IERS Reference Meridian travelling east, consists of parts of northern Norway ( ...

, the Sun appears to move from left to right. In

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean (also known as the Antarctic Ocean), it contains the geographic South Pole. ...

, the equivalent apparent motion is from right to left. This occurs at latitudes ranging from approximately 65°44' to exactly 90° north or south, and does not stop exactly at the

or the Antarctic Circle, due to

refraction In physics, refraction is the redirection of a wave as it passes from one transmission medium, medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commo ...

. The opposite phenomenon,

polar night Polar night is a phenomenon that occurs in the polar regions of Earth, northernmost and southernmost regions of Earth when the Sun remains below the horizon for more than 24 hours. This only occurs inside the polar circles. The opposite phen ...

, occurs in winter, when the Sun stays below the

horizon The horizon is the apparent curve that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This curve divides all viewing directions based on whethe ...

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

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

(

Yukon Yukon () is a Provinces and territories of Canada, territory of Canada, bordering British Columbia to the south, the Northwest Territories to the east, the Beaufort Sea to the north, and the U.S. state of Alaska to the west. It is Canada’s we ...

Nunavut Nunavut is the largest and northernmost Provinces and territories of Canada#Territories, territory of Canada. It was separated officially from the Northwest Territories on April 1, 1999, via the ''Nunavut Act'' and the Nunavut Land Claims Agr ...

, and

Northwest Territories The Northwest Territories is a federal Provinces and territories of Canada, territory of Canada. At a land area of approximately and a 2021 census population of 41,070, it is the second-largest and the most populous of Provinces and territorie ...

Finland Finland, officially the Republic of Finland, is a Nordic country in Northern Europe. It borders Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of Bothnia to the west and the Gulf of Finland to the south, ...

Greenland Greenland is an autonomous territory in the Danish Realm, Kingdom of Denmark. It is by far the largest geographically of three constituent parts of the kingdom; the other two are metropolitan Denmark and the Faroe Islands. Citizens of Greenlan ...

Iceland Iceland is a Nordic countries, Nordic island country between the Atlantic Ocean, North Atlantic and Arctic Oceans, on the Mid-Atlantic Ridge between North America and Europe. It is culturally and politically linked with Europe and is the regi ...

Norway Norway, officially the Kingdom of Norway, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. The remote Arctic island of Jan Mayen and the archipelago of Svalbard also form part of the Kingdom of ...

Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...

Sweden Sweden, formally the Kingdom of Sweden, is a Nordic countries, Nordic country located on the Scandinavian Peninsula in Northern Europe. It borders Norway to the west and north, and Finland to the east. At , Sweden is the largest Nordic count ...

, and the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

(state of

Alaska Alaska ( ) is a non-contiguous U.S. state on the northwest extremity of North America. Part of the Western United States region, it is one of the two non-contiguous U.S. states, alongside Hawaii. Alaska is also considered to be the north ...

). 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. 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 The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is the point in the Northern Hemisphere where the Earth's rotation, Earth's axis of rotation meets its surface. It is called the True North Pole to distingu ...

has midnight sun for about 6 months, from approximately 18 March to 24 September.

South Pole The South Pole, also known as the Geographic South Pole or Terrestrial South Pole, is the point in the Southern Hemisphere where the Earth's rotation, Earth's axis of rotation meets its surface. It is called the True South Pole to distinguish ...

has midnight sun and experiences this from approximately 20 September to 23 March (about 6 months).

Polar circle proximity

Due to 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

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 The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Northwestern Europe, off the coast of European mainland, the continental mainland. It comprises England, Scotlan ...

(and places at similar latitudes, such as

Saint Petersburg Saint Petersburg, formerly known as Petrograd and later Leningrad, is the List of cities and towns in Russia by population, second-largest city in Russia after Moscow. It is situated on the Neva, River Neva, at the head of the Gulf of Finland ...

) experience twilight throughout the night in the northern sky at around the summer solstice. Places sufficiently close to the poles, such as Alert, Nunavut, experience times where it does not get entirely dark at night yet the Sun does not rise either, combining effects of midnight sun and polar night, reaching civil twilight during the "day" and astronomical twilight at "night".

White nights

Locations where the Sun remains less than 6 (or 7

Great Soviet Encyclopedia The ''Great Soviet Encyclopedia'' (GSE; , ''BSE'') is one of the largest Russian-language encyclopedias, published in the Soviet Union from 1926 to 1990. After 2002, the encyclopedia's data was partially included into the later ''Great Russian Enc ...

) degrees below the horizonbetween about 60° 34’ (or 59° 34’) latitude and the polar circleexperience midnight twilight 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. Admiralty Embankment of Neva River in Saint Petersburg during the White nightsIMG 4236

Admiralty Embankment of Neva River in Saint Petersburg during the White nightsIMG 4236

White Nights have become a common symbol of Saint Petersburg, Russia, where they occur from about 11 June to 1 July, and the last 10 days of June are celebrated with cultural events known as the White Nights Festival. The phenomenon carries similar significance for Fairbanks, Alaska, where an annual Midnight Sun Game

baseball Baseball is a bat-and-ball games, bat-and-ball sport played between two team sport, teams of nine players each, taking turns batting (baseball), batting and Fielding (baseball), fielding. The game occurs over the course of several Pitch ...

competition has been contested since 1906 in the twilight surrounding midnight on June 21. The northernmost tip of Antarctica also experiences white nights near the Southern Hemisphere summer solstice.

Explanation

Since the

axial tilt In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane; equivalently, it is the angle between its equatorial plane and orbita ...

of Earth is considerable (23 degrees, 26 minutes, 21.41196 seconds), at high latitudes the Sun does not set in summer; rather, it remains continuously visible for one day during the summer solstice at the polar circle, for several weeks only 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 A solar equinox is a moment in time when the Sun appears directly above the equator, rather than to its north or south. On the day of the equinox, the Sun appears to rise directly east and set directly west. This occurs twice each year, arou ...

es. 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 spiraling higher and reaching its highest circuit of the sky at the summer solstice, before beginning to sink lower, setting just after the autumnal equinox.

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

time zone A time zone is an area which observes a uniform standard time for legal, Commerce, commercial and social purposes. Time zones tend to follow the boundaries between Country, countries and their Administrative division, subdivisions instead of ...

s and the observance of

daylight saving time Daylight saving time (DST), also referred to as daylight savings time, daylight time (Daylight saving time in the United States, United States and Daylight saving time in Canada, Canada), or summer time (British Summer Time, United Kingdom, ...

. For instance, in Fairbanks, Alaska, which is south of the Arctic Circle, the Sun sets at 12:47a.m. at the summer solstice. This is because Fairbanks is 51 minutes (1 hour and 51 minutes at Daylight Savings Time) ahead of its idealized time zone (as most of the state is in one time zone) and Alaska observes daylight saving time. (Fairbanks is at about 147.72 degrees west, corresponding to UTC−9 hours 51 minutes, and is on UTC−9 in winter.) This means that solar culmination occurs at about 12:51p.m. instead of at 12 noon. Also in Fairbanks, Alaska, solar midnight occurs at 01:51 a.m. local time. If a precise moment for the genuine "midnight sun" is required, the observer's

longitude Longitude (, ) is a geographic coordinate that specifies the east- west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek lett ...

, the local

civil time In modern usage, civil time refers to statutory time as designated by civilian authorities. Modern civil time is generally national standard time in a time zone at a UTC offset, fixed offset from Coordinated Universal Time (UTC), possibly adjusted ...

, 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 Coordinated Universal Time (UTC) is the primary time standard globally used to regulate clocks and time. It establishes a reference for the current time, forming the basis for civil time and time zones. UTC facilitates international communicat ...

(UTC, also known as GMT) makes the moment an hour later. These two effects must be added. Furthermore, 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. As an example, at the North Cape of

at midnight on June 21/22, the longitude of 25.9 degrees east makes the moment 103.2 minutes earlier by clock time; but the local time, 2 hours ahead of GMT in the summer, makes it 120 minutes later by clock time. The equation of time at that date is -2.0 minutes. Therefore, the Sun's lowest elevation occurs 120 - 103.2 + 2.0 minutes after midnight: at 00.19 Central European Summer time. 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. 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 outside the polar circle, as described below, and the exact latitudes of the furthest 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 Continental Europe or mainland Europe is the contiguous mainland of Europe, excluding its surrounding islands. It can also be referred to ambiguously as the European continent, – which can conversely mean the whole of Europe – and, by som ...

, midnight sun lasts approximately from 14 May to 29 July. On the

Svalbard Svalbard ( , ), previously known as Spitsbergen or Spitzbergen, is a Norway, Norwegian archipelago that lies at the convergence of the Arctic Ocean with the Atlantic Ocean. North of continental Europe, mainland Europe, it lies about midway be ...

archipelago further north, it lasts from 20 April to 22 August.Trygve B. Haugan, ed. ''Det Nordlige Norge Fra Trondheim Til Midnattssolens Land'' (Trondheim: Reisetrafikkforeningen for Trondheim og Trøndelag. 1940)

Southern and Northern poles

Also, the periods of polar day and polar night are unequal in both polar regions because the Earth is at perihelion in early January and at aphelion in early July. As a result, the polar day is longer than the polar night in the Northern Hemisphere (at Utqiagvik, Alaska, for example, polar day lasts 84 days, while polar night lasts only 68 days), while in the Southern Hemisphere, the situation is the reverse—the polar night is longer than the polar day. 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. Optical effect march sunset - NOAA

References

External links

What is the secret behind midnight sun in Norway
{{DEFAULTSORT:Midnight Sun Earth phenomena Geography of the Arctic Sun Summer solstice