Midnight sun

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Midnight sun at the North Cape on the island of Mageroya in Norway Midnight sun.jpg
Midnight sun at the North Cape on the island of Magerøya in Norway

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. When the midnight sun is seen in the Arctic, the Sun appears to move from left to right, but in Antarctica the equivalent apparent motion is from right to left. This occurs at latitudes from 65°44' to 90° north or south, and does not stop exactly at the Arctic Circle or the Antarctic Circle, due to refraction.

Contents

The opposite phenomenon, polar night, occurs in winter, when the Sun stays below the horizon throughout the day.

Details

Multiple exposure of the midnight sun on Lake Ozhogino in Yakutia, Russia Poliarnyi den' nad oz. Ozhogino.jpg
Multiple exposure of the midnight sun on Lake Ozhogino in Yakutia, Russia

Around the summer solstice (approximately 21 June in the Northern Hemisphere and 21 December in the Southern Hemisphere), in certain areas the Sun does not set below the horizon within a 24-hour period.

Geography

Timelapse video of Lapland's midnight sun in Rovaniemi, Finland

Because there are no permanent human settlements south of the Antarctic Circle, apart from research stations, the countries and territories whose populations experience the midnight sun are limited to those crossed by polar circles: Canada (Yukon, Nunavut, and Northwest Territories), United States (state of Alaska); the nations of Iceland, Finland, Norway, Sweden, Denmark (Greenland), and Russia.

The largest city of the world north of the Arctic Circle, Murmansk (Russia), experiences the 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 6 months from late March to late September.

Polar circle proximity

Because of atmospheric refraction, and also because the Sun is a disc rather than a point, the 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 Alert, Nunavut, experience times where it does not get entirely dark at night yet the Sun does not rise either, combining effects of the midnight sun and polar night, for example where during the "day" it reaches civil twilight and at "night" only reaches astronomical twilight.

White nights

Locations where the Sun remains less than 6 (or 7 [2] ) degrees below the horizon between 60° 34’ (or 59° 34’) latitude and the polar circle experience midnight civil twilight instead of midnight sun, 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 11 June to 2 July, [2] 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; [3] 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, the 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

Summer night in the city of Pori on July 2, 2010 Pori at Night - panoramio.jpg
Summer night in the city of Pori on July 2, 2010

The term "midnight sun" refers to the consecutive 24-hour periods of sunlight experienced in the 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 zones and the observance of daylight saving time. For instance, in Fairbanks, Alaska, which is south of the Arctic Circle, the Sun sets at 12:47 a.m. at the summer solstice. This is because Fairbanks is 51 minutes 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 12:51 p.m. instead of at 12 noon.

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 (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. [4]

As an example, at the North Cape of Norway 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.

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

Duration

The number of days per year with potential midnight sun increases the closer one goes towards either pole. Although approximately defined by the polar circles, in practice the midnight sun can be seen as much as 90 km (55 miles) 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.

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 the 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, the midnight sun lasts approximately from 14 May to 29 July. On the Svalbard archipelago farther north, it lasts from 20 April to 22 August. [5]

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.

Related Research Articles

<span class="mw-page-title-main">Declination</span> Astronomical coordinate analogous to latitude

In astronomy, declination is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declination's angle is measured north or south of the celestial equator, along the hour circle passing through the point in question.

A solar equinox is a moment in time when the Sun crosses the Earth's equator, which is to say, appears directly above the equator, rather than north or south of the equator. On the day of the equinox, the Sun appears to rise "due east" and set "due west". This occurs twice each year, around 20 March and 23 September.

A solstice is an event that occurs when the Sun appears to reach its most northerly or southerly excursion relative to the celestial equator on the celestial sphere. Two solstices occur annually, around June 21 and December 21. In many countries, the seasons of the year are determined by the solstices and the equinoxes.

<span class="mw-page-title-main">Circle of latitude</span> Geographic notion

A circle of latitude or line of latitude on Earth is an abstract east–west small circle connecting all locations around Earth at a given latitude coordinate line.

<span class="mw-page-title-main">Polar circle</span> Circle of latitude

A polar circle is a geographic term for a conditional circular line (arc) referring either to the Arctic Circle or the Antarctic Circle. These are two of the keynote circles of latitude (parallels). On Earth, the Arctic Circle is currently drifting northwards at a speed of about 14.5 m per year and is now at a mean latitude of 66°33′49.3″ N; the Antarctic Circle is currently drifting southwards at a speed of about 14.5 m per year and is now at a mean latitude of 66°33′49.3″ S. Polar circles are often equated with polar regions of Earth. Due to their inherent climate environment, the bulk of the Arctic Circle, much of which is sea, is sparsely settled whereas this applies to all of Antarctica which is mainly land and sheltered ice shelves.

In observational astronomy, culmination is the passage of a celestial object across the observer's local meridian. These events were also known as meridian transits, used in timekeeping and navigation, and measured precisely using a transit telescope.

<span class="mw-page-title-main">Sunset</span> Daily falling of the Sun below the horizon

Sunset, also known as sundown, is the daily disappearance of the Sun below the horizon due to Earth's rotation. As viewed from everywhere on Earth, the equinox Sun sets due west at the moment of both the spring and autumn equinoxes. As viewed from the Northern Hemisphere, the Sun sets to the northwest in the spring and summer, and to the southwest in the autumn and winter; these seasons are reversed for the Southern Hemisphere.

<span class="mw-page-title-main">Dawn</span> Time that marks the beginning of the twilight before sunrise

Dawn is the time that marks the beginning of twilight before sunrise. It is recognized by the appearance of indirect sunlight being scattered in Earth's atmosphere, when the centre of the Sun's disc has reached 18° below the observer's horizon. This morning twilight period will last until sunrise, when direct sunlight outshines the diffused light.

<span class="mw-page-title-main">Night</span> Period of darkness during a 24-hour day

Night is the period of ambient darkness from sunset to sunrise during each 24-hour day, when the Sun is below the horizon. The exact time when night begins and ends depends on the location and varies throughout the year, based on factors such as season and latitude.

<span class="mw-page-title-main">Twilight</span> Illumination of the atmosphere when the sun is not directly visible because it is below the horizon

Twilight is light produced by sunlight scattering in the upper atmosphere, when the Sun is below the horizon, which illuminates the lower atmosphere and the Earth's surface. The word twilight can also refer to the periods of time when this illumination occurs.

<span class="mw-page-title-main">Polar night</span> Night lasting for more than 24 hours

The polar night is a phenomenon where the nighttime lasts for more than 24 hours that occurs in the northernmost and southernmost regions of Earth. This occurs only inside the polar circles. The opposite phenomenon, the polar day, or midnight sun, occurs when the Sun remains above the horizon for more than 24 hours.

The five main latitude regions of Earth's surface comprise geographical zones, divided by the major circles of latitude. The differences between them relate to climate. They are as follows:

  1. The North Frigid Zone, between the North Pole at 90° N and the Arctic Circle at 66°33′48.7" N, covers 4.12% of Earth's surface.
  2. The North Temperate Zone, between the Arctic Circle at 66°33′48.7" N and the Tropic of Cancer at 23°26'11.3" N, covers 25.99% of Earth's surface.
  3. The Torrid Zone, between the Tropic of Cancer at 23°26'11.3" N and the Tropic of Capricorn at 23°26'11.3" S, covers 39.78% of Earth's surface.
  4. The South Temperate Zone, between the Tropic of Capricorn at 23°26'11.3" S and the Antarctic Circle at 66°33'48.7" S, covers 25.99% of Earth's surface.
  5. The South Frigid Zone, from the Antarctic Circle at 66°33'48.7" S and the South Pole at 90° S, covers 4.12% of Earth's surface.
<span class="mw-page-title-main">Daytime</span> Period of a day in which a location experiences natural illumination

Daytime as observed on Earth is the period of the day during which a given location experiences natural illumination from direct sunlight. Daytime occurs when the Sun appears above the local horizon, that is, anywhere on the globe's hemisphere facing the Sun. In direct sunlight the movement of the sun can be recorded and observed using a sundial that casts a shadow that slowly moves during the day. Other planets and natural satellites that rotate relative to a luminous primary body, such as a local star, also experience daytime, but this article primarily discusses daytime on Earth.

<span class="mw-page-title-main">Sun path</span> Arc-like path that the Sun appears to follow across the sky

Sun path, sometimes also called day arc, refers to the daily and seasonal arc-like path that the Sun appears to follow across the sky as the Earth rotates and orbits the Sun. The Sun's path affects the length of daytime experienced and amount of daylight received along a certain latitude during a given season.

<span class="mw-page-title-main">Inuit astronomy</span> Inuit beliefs about the celestial sphere or Qilak

Inuit astronomy is centered around the Qilak, the Inuit name for the celestial sphere and the home for souls of departed people. Inuit beliefs about astronomy are the shaped by the harsh climate in the Arctic and the resulting difficulties of surviving and hunting in the region. The stars were an important tool to track time, seasons, and location, particularly during winter.

<span class="mw-page-title-main">Equator</span> Line halfway between North and South poles

The equator is a circle of latitude, about 40,075 km (24,901 mi) in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles.

<span class="mw-page-title-main">Season</span> Subdivision of the year based on orbit and axial tilt

A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. On Earth, seasons are the result of the axial parallelism of Earth's tilted orbit around the Sun. In temperate and polar regions, the seasons are marked by changes in the intensity of sunlight that reaches the Earth's surface, variations of which may cause animals to undergo hibernation or to migrate, and plants to be dormant. Various cultures define the number and nature of seasons based on regional variations, and as such there are a number of both modern and historical cultures whose number of seasons varies.

<span class="mw-page-title-main">Time in Antarctica</span> Time zones in Antarctica

Antarctica sits on every line of longitude because the South Pole is on the continent. Theoretically, Antarctica would be located in all time zones; however, areas south of the Antarctic Circle experience extreme day-night cycles near the times of the June and December solstices, making it difficult to determine which time zone would be appropriate. For practical purposes time zones are usually based on territorial claims; however, many stations use the time of the country they are owned by or the time zone of their supply base. Nearby stations can have different time zones because they belong to different countries. Many areas have no time zone since nothing is decided and there are not even any temporary settlements that have any clocks. They are simply labeled with UTC time.

<span class="mw-page-title-main">Antarctic Circle</span> Boundary of the Antarctic

The Antarctic Circle is the most southerly of the five major circles of latitude that mark maps of Earth. The region south of this circle is known as the Antarctic, and the zone immediately to the north is called the Southern Temperate Zone. South of the Antarctic Circle, the Sun is above the horizon for 24 continuous hours at least once per year and the centre of the Sun is below the horizon for 24 continuous hours at least once per year ; this is also true within the equivalent polar circle in the Northern Hemisphere, the Arctic Circle.

<span class="mw-page-title-main">Arctic Circle</span> Boundary of the Arctic

The Arctic Circle is one of the two polar circles, and the most northerly of the five major circles of latitude as shown on maps of Earth. Its southern equivalent is the Antarctic Circle.

References

  1. Nuorgam, Lapland, Finland — Sunrise, Sunset, and Daylength, May 2022
  2. 1 2 Great Soviet Encyclopedia
  3. "What is the Midnight Sun Phenomenon? | Earth Phenomena | Planetary Science". Scribd. Retrieved 2017-08-25.
  4. H. Spencer Jones, General Astronomy (Edward Arnold, London, 1922), Chapters I-III
  5. Trygve B. Haugan, ed. Det Nordlige Norge Fra Trondheim Til Midnattssolens Land (Trondheim: Reisetrafikkforeningen for Trondheim og Trøndelag. 1940)

Further reading