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37-740: The river flows south of the Arctic Circle , across desolate tundra territories of the Oymyakonsky District marked by mountainous terrain and permafrost . The Khastakh is a left tributary of the Indigirka. It has its sources in the southern slopes of the Khalkan Range (Халканский хребет), a subrange of the Suntar-Khayata , by the border with Okhotsky District of Khabarovsk Krai . The river flows roughly in

74-462: A mental illness prior to the study. While in Antarctica, 7 of the 88 crew members were diagnosed with a mental illness during early winter. The mental illnesses included insomnia disorder (3 diagnosed), depressive disorder (1 diagnosed), adjustment disorder (2 diagnosed), and alcohol use disorder (1 diagnosed). Overall, both Antarctic studies showed a lower amount of sleep beginning at

111-627: A margin of more than 2° over a 41,000-year period, owing to tidal forces resulting from the orbit of the Moon . Consequently, the Arctic Circle is currently drifting northwards at a speed of about 14.5 m (48 ft) per year. The word arctic comes from the Greek word ἀρκτικός ( arktikos : "near the Bear , northern") and that from the word ἄρκτος ( arktos : " bear "). The Arctic Circle

148-596: A northern direction into a basin of the Yana-Oymyakon Highlands filled with lakes where it meanders and divides into multiple channels. Finally the river joins the Taryn-Yuryakh flowing from the right to form the head of the Indigirka 1,726 km (1,072 mi) from its mouth. The total length of the Indigirka counting the Khastakh is 1,977 km (1,228 mi). The main tributaries of

185-470: A river in the Russian Far East is a stub . You can help Misplaced Pages by expanding it . This Sakha Republic location article is a stub . You can help Misplaced Pages by expanding it . Arctic Circle 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 at about 66° 34' N. Its southern equivalent

222-523: Is a 2 month long polar night, lasting from mid-November to mid-January. An analysis was conducted based on 2015-16 data from a health survey that involved residents of the region over age 40, with the goal being to analyze the seasonal variation of sleeping patterns in Tromsø. The study found that there was a higher prevalence of insomnia among men in the fall and winter months, but not among women. However, overall, sleep duration varied little to none throughout

259-1247: Is a location at the horizon with more light than others around midday due to refraction. Some critical observations, such as of faint diffuse items such as nebulae and galaxies , may require observations beyond the limit of astronomical twilight. Nautical twilight happens when the Sun is between 6 and 12° degrees below the horizon, so this phenomenon can also be referred to as nautical polar night. The Norwegian territory of Ny-Ålesund , Svalbard , experiences this from about December 12 to 30. Its antipode ( 78°55′S 168°4′W  /  78.917°S 168.067°W  / -78.917; -168.067 ) experiences this from about June 12 to July 1. The Canadian territory of Eureka, Nunavut , experiences this from about December 2 to January 8. Its antipode ( 79°59′S 94°4′E  /  79.983°S 94.067°E  / -79.983; 94.067 ) experiences this from about June 1 to July 11. The Russian territory of Franz Josef Land experiences this from about November 27 to January 15. Its antipode ( 81°S 125°W  /  81°S 125°W  / -81; -125 ) experiences this from about May 25 to July 17. Alert , Nunavut ,

296-407: Is a period of continuous night where no astronomical twilight occurs at the solar culmination . During a true polar night, stars of the sixth magnitude, which are the dimmest stars visible to the naked eye, will be visible throughout the entire 24-hour day . At solar noon , the sun will be between exactly 18° and approximately 23° 26' below the horizon. These conditions last for about 11 weeks at

333-431: Is defined as when it is darker than the corresponding kind of twilight. The descriptions below are based on relatively clear skies, so the sky will be darker in the presence of dense clouds. As mentioned, a location experiencing polar night does not mean that the location will be in full darkness; in most cases, due to sunlight being refracted over the horizon, a location experiencing polar night will actually be in one of

370-419: Is exactly 12° to 18° inside the polar circles. There is then no nautical twilight at the solar culmination , only astronomical twilight . During astronomical polar twilight, the sky is dark enough at midday to permit astronomical observation of point sources of light such as stars , except in regions with more intense skyglow due to light pollution , moonlight , auroras , and other sources of light. There

407-524: Is longer than polar night, and the area that experiences polar night is somewhat smaller than the area that experiences polar day. The polar circles are located at latitudes between these two areas, at approximately 66.5°. While it is day in the Arctic Circle , it is night in the Antarctic Circle , and vice versa. Any planet or moon with a sufficient axial tilt that rotates with respect to its star significantly more frequently than it orbits

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444-694: Is the Amundsen–Scott scientific research station in Antarctica , whose winter personnel are completely isolated from mid-February to late October. The South Pole experiences this from about May 11 to August 1, while the North Pole experiences this from about November 12 to January 28. If an observer located on either the North Pole or the South Pole were to define a "day" as the time from

481-604: Is the Antarctic Circle . The Arctic Circle marks the southernmost latitude at which, on the winter solstice (which is the shortest day of the year) in the Northern Hemisphere , the Sun will not rise all day, and on the Northern Hemisphere's summer solstice (which is the longest day of the year), the Sun will not set. These phenomena are referred to as polar night and midnight sun respectively, and

518-549: Is the largest settlement in the immediate vicinity of the Arctic Circle, lying 6 km (4 mi) south of the line. Salekhard (51,186) in Russia is the only city in the world located directly on the Arctic Circle. In contrast, the largest North American community north of the Arctic Circle, Sisimiut ( Greenland ), has approximately 5,600 inhabitants. In the United States, Utqiagvik, Alaska (formerly known as Barrow)

555-639: Is the largest settlement north of the Arctic Circle with about 5,000 inhabitants. The largest such community in Canada is Inuvik in the Northwest Territories , with 3,137 inhabitants. Download coordinates as: The Arctic Circle is roughly 16,000 km (9,900 mi) in circumference. The area north of the Circle is about 20,000,000 km (7,700,000 sq mi) and covers roughly 4% of Earth's surface. The Arctic Circle passes through

592-448: Is the southernmost latitude in the Northern Hemisphere at which the centre of the Sun can remain continuously above or below the horizon for twenty-four hours; as a result, at least once each year at any location within the Arctic Circle the centre of the Sun is visible at local midnight , and at least once the centre is not visible at local noon . Directly on the Arctic Circle these events occur, in principle, exactly once per year: at

629-747: Is this definition met. The Norwegian territory of Longyearbyen , Svalbard , experiences nautical polar twilight from about 11 November until 30 January. Dikson , in Russia, experiences nautical polar twilight from about 6 December to 6 January. During dense cloud cover, places like the coast of Finnmark (about 70°) in Norway will experience a "day" that is darker than usual. On the Canadian territory of Pond Inlet, Nunavut , however, nautical polar twilight lasts from about 16 December until 26 December. Astronomical polar twilight occurs at latitudes between about 78° 34' and 84° 34' North or South, which

666-545: The Arctic Ocean , the Scandinavian Peninsula , North Asia , Northern America , and Greenland. The land within the Arctic Circle is divided among eight countries: Norway, Sweden, Finland, Russia, the United States ( Alaska ), Canada ( Yukon , Northwest Territories , and Nunavut ), Denmark (Greenland), and Iceland (where it passes through the small offshore island of Grímsey ). The climate north of

703-473: The June and December solstices , respectively. However, because of atmospheric refraction and mirages , and also because the sun appears as a disk and not a point, part of the midnight sun is visible, on the night of the northern summer solstice , at a latitude of about 50 minutes of arc (′) (90 km (56 mi)) south of the Arctic Circle. Similarly, on the day of the northern winter solstice , part of

740-611: The solar culmination , only civil twilight . During civil polar twilight, there is still enough light for most normal outdoor activities at midday because of light scattering by the upper atmosphere and refraction. However, street lamps may still remain on, and a person looking at a window from within a brightly lit room might see their reflection even at midday, as the level of outdoor illuminance will still be below that of many illuminated indoor spaces. Northern Hemisphere: Southern Hemisphere: Sufferers of seasonal affective disorder tend to seek out therapy with artificial light, as

777-473: The 2010s, bringing in a total of 82 participants. The study found that participants generally slept for longer periods of time in the summer months than the winter months. Additionally, greater amounts of social jetlag were observed in the winter months. A third study aimed to examine the mental health of 88 Korean crew members at two different research stations in Antarctica, King Sejong Station and Jang Bogo Station . No crew members had been diagnosed with

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814-526: The Arctic Circle is generally cold, but the coastal areas of Norway have a generally mild climate as a result of the Gulf Stream , which makes the ports of northern Norway and northwest Russia ice-free all year long. In the interior, summers can be quite warm, while winters are extremely cold. For example, summer temperatures in Norilsk , Russia will sometimes reach as high as 30 °C (86 °F), while

851-399: The Khastakh are the 132 km (82 mi) long Buor-Yuryakh on the right, as well as the 82 km (51 mi) long Burgachen and the 107 km (66 mi) long Labynkyr on the left. The river is frozen between the beginning of October and the end of May. There are more than 1,900 lakes in its basin with a total area of 145 km (56 sq mi). This article related to

888-411: The Sun is 12 degrees below the horizon. During nautical twilight, the horizon is visible enough for navigation. "Astronomical" twilight continues until the Sun has sunk 18 degrees below the horizon. Beyond 18 degrees, refracted sunlight is no longer visible. True night is defined as the period when the sun is 18 or more degrees below either horizon. Since the atmosphere refracts sunlight, polar day

925-675: The Sun may be seen up to about 50′ north of the Arctic Circle. That is true at sea level ; those limits increase with elevation above sea level , although in mountainous regions there is often no direct view of the true horizon. The largest communities north of the Arctic Circle are situated in Russia, Norway, and Sweden: Murmansk (population 295,374) and Norilsk (178,018) in Russia; Tromsø (75,638) in Norway, Vorkuta (58,133) in Russia, Bodø (52,357) and Harstad (24,703) in Norway; and Kiruna , Sweden (22,841). Rovaniemi (62,667) in Finland

962-400: The Sun remains above the horizon for more than 24 hours. There are multiple ways to define twilight, the gradual transition to and from darkness when the Sun is below the horizon. "Civil" twilight occurs when the Sun is between 0 and 6 degrees below the horizon. Nearby planets like Venus and bright stars like Sirius are visible during this period. "Nautical" twilight continues until

999-589: The further north one progresses, the more pronounced these effects become. For example, in the Russian port city of Murmansk , three degrees above the Arctic Circle, the Sun does not rise above the horizon for 40 successive days in midwinter. The position of the Arctic Circle is not fixed and currently runs 66°33′50.2″ north of the Equator . Its latitude depends on the Earth's axial tilt , which fluctuates within

1036-421: The last). Following civil twilight, the day will progress through the other phases in the opposite order (nautical twilight, then astronomical twilight, then night to end the day). Civil polar twilight occurs at latitudes between about 67°24' and 72°34' North or South, where the Sun will be below the horizon all day on the winter solstice , but by less than 6° at solar noon . There is then no true daylight at

1073-407: The maximal elevation of the Sun above the horizon during one period of daylight, until the maximal elevation of the Sun above the horizon of the next period of daylight, then a "polar day" as experienced by such an observer would be one Earth-year long. Numerous analyses have been conducted to examine the effects of polar night on humans. In Tromsø, Norway , a city located at 69 degrees north, there

1110-672: The northernmost settlement in Canada and the world, experiences this from about November 19 to January 22. Its antipode ( 82°30′S 117°38′E  /  82.500°S 117.633°E  / -82.500; 117.633 ) experiences this from about May 19 to July 25. Oodaaq , a gravel bank at the northern tip of Greenland and a disputed northernmost point of land , experiences this from about November 15 to January 27. Its antipode ( 83°40′S 150°7′E  /  83.667°S 150.117°E  / -83.667; 150.117 ) experiences this from about May 13 to July 31. A true polar night

1147-439: The polar circles. There is then no civil twilight at the solar culmination , only nautical twilight . During nautical polar twilight, the human eye may distinguish general outlines of ground objects at midday but cannot participate in detailed outdoor operations. Civil twilight happens when the Sun is between 0 and 6° below the horizon, so this phenomenon can also be referred to as civil polar night. Nowhere on mainland Europe

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1184-441: The poles. Astronomical twilight happens when the Sun is between twelve and eighteen degrees below the horizon, so this phenomenon can also be referred to as astronomical polar night. Thus, the true polar night is limited to latitudes above roughly 84° 34' North or South, which is exactly 18° within the polar circles, or approximately five and a half degrees from the poles. The only permanent settlement on Earth at these latitudes

1221-416: The psychological benefits of daylight require relatively high levels of ambient light (up to 10,000  lux ) which are not present in any stage of twilight; thus, the midday twilights experienced anywhere inside the polar circles are still "polar nights" for this purpose. Nautical polar twilight occurs at latitudes between about 72° 34' and 78° 34' North or South, which is exactly 6° to 12° inside

1258-416: The star (and with no tidal locking between the two) will experience the same phenomenon (a nighttime lasting more than one rotation period). The length of polar night varies by latitude from 24 hours just inside the polar circles to 179 days at the poles. As there are various kinds of twilight , there also exist various kinds of polar twilight that progress towards true polar night. Each kind of polar night

1295-456: The various phases of polar twilight. As in locations experiencing daylight, the middle of the day will typically be the brightest time in locations experiencing polar twilight. For example, a typical day during civil polar twilight in Vadsø, Norway will begin with night, astronomical twilight, nautical twilight, and civil twilight in that order (with each successive phase including more light than

1332-469: The winter temperatures frequently fall below −50 °C (−58 °F). Starting at the prime meridian and heading eastwards, the Arctic Circle passes through: Polar night Polar night is a phenomenon that occurs in the 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 phenomenon, polar day or midnight sun , occurs when

1369-446: The year despite the extreme changes in daylight; it is worthwhile to note that a factor in this result may be the significant amount of artificial light in Tromsø. A similar study was conducted among men who overwintered at Belgrano II , an Argentine research station in Antarctica . The station is located at 77 degrees south, resulting in a polar night 4 months in length. The study was conducted across 5 different winter campaigns in

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