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100-457: The ultraviolet radiation in sunlight has both positive and negative health effects, as it is both a requisite for vitamin D 3 synthesis and a mutagen . Sunlight takes about 8.3 minutes to reach Earth from the surface of the Sun. A photon starting at the center of the Sun and changing direction every time it encounters a charged particle would take between 10,000 and 170,000 years to get to

200-633: A Historic Site or Monument (HSM 1) following a proposal by Argentina to the Antarctic Treaty Consultative Meeting . In 1820, several expeditions claimed to have been the first to have sighted Antarctica, with the first being the Russian expedition led by Fabian Gottlieb von Bellingshausen and Mikhail Lazarev . The first landing was probably just over a year later when English-born American captain John Davis ,

300-409: A broad range of wavelengths: X-rays , ultraviolet , visible light , infrared , and radio waves . Different depths in the photosphere have different temperatures, and this partially explains the deviations from a black-body spectrum. There is also a flux of gamma rays from the quiescent sun, obeying a power law between 0.5 and 2.6 TeV . Some gamma rays are caused by cosmic rays interacting with

400-488: A key role in recombinational repair of DNA damage. Thus the level of terrestrial solar UV-B radiation likely affects genome stability in plants. Vitamin D3 Cholecalciferol , also known as vitamin D 3 or colecalciferol , is a type of vitamin D that is produced by the skin when exposed to UVB light ; it is found in certain foods and can be taken as a dietary supplement . Cholecalciferol

500-561: A less clear, and probably more complicated fashion, with Earth's climate responses than earlier assumed, fueling broad avenues of new research in "the connection of the Sun and stratosphere, troposphere, biosphere, ocean, and Earth's climate". The spectrum of surface illumination depends upon solar elevation due to atmospheric effects, with the blue spectral component dominating during twilight before and after sunrise and sunset, respectively, and red dominating during sunrise and sunset. These effects are apparent in natural light photography where

600-657: A matter of practical convenience the Amundsen–Scott South Pole Station keeps New Zealand Time (UTC+12/UTC+13). This is because the US flies its resupply missions (" Operation Deep Freeze ") out of McMurdo Station , which is supplied from Christchurch , New Zealand. Due to its exceptionally harsh climate, there are no native resident plants or animals at the South Pole. Off-course south polar skuas and snow petrels are occasionally seen there. In 2000 it

700-428: A nearly perfect circle, and at other times stretching out to an orbital eccentricity of 5% (currently 1.67%). As the orbital eccentricity changes, the average distance from the Sun (the semimajor axis does not significantly vary, and so the total insolation over a year remains almost constant due to Kepler's second law , where A {\displaystyle A} is the "areal velocity" invariant. That is,

800-463: A number of states in the world. For many people with light skin, one purpose for sunbathing is to darken one's skin color (get a sun tan), as this is considered in some cultures to be attractive, associated with outdoor activity, vacations/holidays , and health. Some people prefer naked sunbathing so that an "all-over" or "even" tan can be obtained, sometimes as part of a specific lifestyle. Controlled heliotherapy , or sunbathing, has been used as

900-579: A perpendicular surface at sea level. The illumination of a horizontal surface will be considerably less than this if the Sun is not very high in the sky. Averaged over a day, the highest amount of sunlight on a horizontal surface occurs in January at the South Pole (see insolation ). Dividing the irradiance of 1,050 W/m by the size of the Sun's disk in steradians gives an average radiance of 15.4 MW per square metre per steradian. (However,

1000-588: A resin which melts at about room temperature and usually has a potency of 25 000 000 to 30 000 000  International Units/gram . [REDACTED] Cholecalciferol is also produced industrially for use in vitamin supplements from lichens , which is suitable for vegans. Cholecalciferol is very sensitive to UV radiation and will rapidly, but reversibly, break down to form supra-sterols, which can further irreversibly convert to ergosterol . Rodents are somewhat more susceptible to high doses than other species, and cholecalciferol has been used in poison bait for

1100-534: A risk factor for skin cancer, "sun avoidance may carry more of a cost than benefit for over-all good health". A study found that there is no evidence that UV reduces lifespan in contrast to other risk factors like smoking, alcohol and high blood pressure. Elevated solar UV -B doses increase the frequency of DNA recombination in Arabidopsis thaliana and tobacco ( Nicotiana tabacum ) plants. These increases are accompanied by strong induction of an enzyme with

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1200-466: A sealer, set foot on the ice. The basic geography of the Antarctic coastline was not understood until the mid-to-late 19th century. American naval officer Charles Wilkes claimed (correctly) that Antarctica was a new continent, basing the claim on his exploration in 1839–40, while James Clark Ross , in his expedition of 1839–1843, hoped that he might be able to sail all the way to the South Pole; He

1300-454: A single dose, or sometimes in two to four divided doses. There are concerns about the safety of such large doses. Low circulating vitamin D levels have been associated with lower total testosterone levels in males. Vitamin D supplementation could potentially improve total testosterone concentration, although more research is needed. A meta-analysis of 2007 concluded that daily intake of 1000 to 2000 IU/d of vitamin D 3 could reduce

1400-479: A treatment for psoriasis and other maladies. Skin tanning is achieved by an increase in the dark pigment inside skin cells called melanocytes , and is an automatic response mechanism of the body to sufficient exposure to ultraviolet radiation from the Sun or from artificial sunlamps. Thus, the tan gradually disappears with time, when one is no longer exposed to these sources. The ultraviolet radiation in sunlight has both positive and negative health effects, as it

1500-426: A wide range of cholecalciferol dosages, with LD 50 as high as 88 mg/kg or LD Lo as low as 2 mg/kg reported for dogs. Researchers have reported that the compound is less toxic to non-target species than earlier generations of anticoagulant rodenticides ( Warfarin and congeners ) or Bromethalin , and that relay toxicosis (poisoning by eating a poisoned animal) has not been documented. Nevertheless,

1600-553: Is 0.025 μg , or 25 ng . Dietary reference intake values for vitamin D ( ergocalciferol , which is D 2 , or cholecalciferol, which is D 3 ), or both, have been established and recommendations vary depending on the country: Low levels of vitamin D3 are more commonly found in individuals living in northern latitudes or with other reasons for a lack of regular sun exposure, including being housebound, frail, elderly, or obese, having darker skin, and wearing clothes that cover most of

1700-489: Is synthesized by the body during UVB radiation exposure. The three steps in the synthesis and activation of vitamin D 3 are regulated as follows: Cholecalciferol is produced industrially for use in vitamin supplements and to fortify foods . As a pharmaceutical drug it is called cholecalciferol ( USAN ) or colecalciferol ( INN , BAN ). It is produced by the ultraviolet irradiation of 7-dehydrocholesterol extracted from lanolin found in sheep's wool . Cholesterol

1800-553: Is a credible case to consider when making vitamin D intake recommendations. Patients with severe vitamin D deficiency will require treatment with a loading dose ; its magnitude can be calculated based on the actual serum 25-hydroxy-vitamin D level and body weight. There are conflicting reports concerning the relative effectiveness of cholecalciferol (D 3 ) versus ergocalciferol (D 2 ), with some studies suggesting less efficacy of D 2 , and others showing no difference. There are differences in absorption, binding and inactivation of

1900-404: Is a form of vitamin D which is naturally synthesized in skin and functions as a pro-hormone, being converted to calcitriol . This is important for maintaining calcium levels and promoting bone health and development. As a medication, cholecalciferol may be taken as a dietary supplement to prevent or to treat vitamin D deficiency. One gram is 40 000 000 ( 40 × 10 ) IU , equivalently 1 IU

2000-488: Is a measure of flux density , is the amount of incoming solar electromagnetic radiation per unit area that would be incident on a plane perpendicular to the rays, at a distance of one astronomical unit (AU) (roughly the mean distance from the Sun to Earth). The "solar constant" includes all types of solar radiation, not just the visible light . Its average value was thought to be approximately 1,366 W/m, varying slightly with solar activity , but recent recalibrations of

2100-836: Is also added to products like plants, cow milk, fruit juice, yogurt, and margarine. Cholecalciferol can be taken orally as a dietary supplement to prevent vitamin D deficiency or as a medication to treat associated diseases, including rickets . It is also used in the management of familial hypophosphatemia , hypoparathyroidism that is causing low blood calcium , and Fanconi syndrome . Vitamin-D supplements may not be effective in people with severe kidney disease . Excessive doses in humans can result in vomiting, constipation, muscle weakness, and confusion. Other risks include kidney stones . Doses greater than 40 000   IU ( 1000 μg ) per day are generally required before high blood calcium occurs. Normal doses, 800–2000  IU per day, are safe in pregnancy . Cholecalciferol

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2200-476: Is always low in the sky, reaching a maximum of approximately 23.5° around the December solstice because of the approximately 23.5° tilt of the earth's axis. Much of the sunlight that does reach the surface is reflected by the white snow. This lack of warmth from the sun, combined with the high altitude (about 2,800 metres (9,200 ft)), means that the South Pole has one of the coldest climates on Earth (though it

2300-410: Is ample sunlight. Some common places for sunbathing include beaches , open air swimming pools , parks , gardens , and sidewalk cafes . Sunbathers typically wear limited amounts of clothing or some simply go nude . For some, an alternative to sunbathing is the use of a sunbed that generates ultraviolet light and can be used indoors regardless of weather conditions. Tanning beds have been banned in

2400-432: Is both a principal source of vitamin D 3 and a mutagen . A dietary supplement can supply vitamin D without this mutagenic effect, but bypasses natural mechanisms that would prevent overdoses of vitamin D generated internally from sunlight. Vitamin D has a wide range of positive health effects, which include strengthening bones and possibly inhibiting the growth of some cancers. Sun exposure has also been associated with

2500-626: Is distinct from the South Magnetic Pole , the position of which is defined based on Earth's magnetic field . The South Pole is the center of the Southern Hemisphere . 90°S 0°E  /  90°S 0°E  / -90; 0 For most purposes, the Geographic South Pole is defined as the southern point of the two points where Earth's axis of rotation intersects its surface (the other being

2600-409: Is extracted from wool grease and wool wax alcohols obtained from the cleaning of wool after shearing. The cholesterol undergoes a four-step process to make 7-dehydrocholesterol, the same compound that is produced in the skin of animals. The 7-dehydrocholesterol is then irradiated with ultraviolet light. Some unwanted isomers are formed during irradiation: these are removed by various techniques, leaving

2700-569: Is fueled by light from the Sun. Most autotrophs , such as plants, use the energy of sunlight, combined with carbon dioxide and water, to produce simple sugars—a process known as photosynthesis . These sugars are then used as building-blocks and in other synthetic pathways that allow the organism to grow. Heterotrophs , such as animals, use light from the Sun indirectly by consuming the products of autotrophs, either by consuming autotrophs, by consuming their products, or by consuming other heterotrophs. The sugars and other molecular components produced by

2800-441: Is given to a good approximation by where dn=1 on January 1; dn=32 on February 1; dn=59 on March 1 (except on leap years, where dn=60), etc. In this formula dn–3 is used, because in modern times Earth's perihelion , the closest approach to the Sun and, therefore, the maximum E ext occurs around January 3 each year. The value of 0.033412 is determined knowing that the ratio between the perihelion (0.98328989 AU) squared and

2900-552: Is impossible from UV exposure; the skin reaches an equilibrium where the vitamin degrades as fast as it is created. Cholecalciferol can be produced in skin from the light emitted by the UV lamps in tanning beds , which produce ultraviolet primarily in the UVA spectrum, but typically produce 4% to 10% of the total UV emissions as UVB. Levels in blood are higher in frequent users of tanning salons. A 293 nanometer UVB light emitting diode (LED)

3000-499: Is located about 1,300 km (810 mi) from the nearest open sea at the Bay of Whales . The ice is estimated to be about 2,700 m (8,900 ft) thick at the Pole, so the land surface under the ice sheet is actually near sea level. The polar ice sheet is moving at a rate of roughly 10 m (33 ft) per year in a direction between 37° and 40° west of grid north, down towards

3100-466: Is needed; only a handful of objects in the Solar System have been discovered that are known to orbit farther than such a distance, among them 90377 Sedna and (87269) 2000 OO 67 . On Earth, the solar radiation varies with the angle of the Sun above the horizon , with longer sunlight duration at high latitudes during summer, varying to no sunlight at all in winter near the pertinent pole. When

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3200-458: Is not entirely clear how the two are related. Cholecalciferol is one of the five forms of vitamin D . Cholecalciferol is a secosteroid , that is, a steroid molecule with one ring open. By itself cholecalciferol is inactive. It is converted to its active form by two hydroxylations : the first in the liver, by CYP2R1 or CYP27A1 , to form 25-hydroxycholecalciferol ( calcifediol , 25-OH vitamin D 3 ). The second hydroxylation occurs mainly in

3300-597: Is not quite the coldest; that record goes to the region in the vicinity of the Vostok Station , also in Antarctica, which lies at a higher elevation). The South Pole is at an altitude of 9,200 feet (2,800 m) but feels like 11,000 feet (3,400 m). Centripetal force from the spin of the planet throws the atmosphere toward the equator. The South Pole is colder than the North Pole primarily because of

3400-449: Is synthesised in the skin following sunlight exposure. It is then converted in the liver to calcifediol (25-hydroxycholecalciferol D), which is further converted in the kidney to calcitriol (1,25-dihydroxycholecalciferol D). One of calcitriol’s most important functions is to promote calcium uptake by the intestines. Cholecalciferol is present in food such as fatty fish, beef liver, eggs, and cheese. In some countries, cholecalciferol

3500-510: The Commonwealth Trans-Antarctic Expedition . There have been many subsequent expeditions to arrive at the South Pole by surface transportation, including those by Havola, Crary , and Fiennes . The first group of women to reach the pole were Pam Young, Jean Pearson, Lois Jones , Eileen McSaveney , Kay Lindsay, and Terry Tickhill in 1969. In 1978–79, Michele Eileen Raney became the first woman to winter at

3600-553: The Earth's atmosphere spans a range of 100  nm to about 1  mm (1,000,000 nm). This band of significant radiation power can be divided into five regions in increasing order of wavelengths : Tables of direct solar radiation on various slopes from 0 to 60 degrees north latitude, in calories per square centimetre, issued in 1972 and published by Pacific Northwest Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture, Portland, Oregon, USA, appear on

3700-532: The Geographic North Pole ). However, Earth's axis of rotation is actually subject to very small "wobbles" ( polar motion ), so this definition is not adequate for very precise work. The geographic coordinates of the South Pole are usually given simply as 90°S, since its longitude is geometrically undefined and irrelevant. When a longitude is desired, it may be given as 0°. At the South Pole, all directions face north. For this reason, directions at

3800-490: The Weddell Sea . Therefore, the position of the station and other artificial features relative to the geographic pole gradually shift over time. The Geographic South Pole is marked by a stake in the ice alongside a small sign; these are repositioned each year in a ceremony on New Year's Day to compensate for the movement of the ice. The sign records the respective dates that Roald Amundsen and Robert F. Scott reached

3900-532: The electromagnetic spectrum . Although the radiation created in the solar core consists mostly of x rays , internal absorption and thermalization convert these super-high-energy photons to lower-energy photons before they reach the Sun's surface and are emitted out into space. As a result, the photosphere of the Sun does not emit much X radiation ( solar X-rays ), although it does emit such "hard radiations" as X-rays and even gamma rays during solar flares . The quiet (non-flaring) Sun, including its corona , emits

4000-457: The Antarctic coast to the South Pole and back. The two expeditions started from Hercules Inlet a day apart, with Gamme starting first, but completing according to plan the last few kilometers together. As Gamme traveled alone he thus simultaneously became the first to complete the task solo. On 28 December 2018, Captain Lou Rudd became the first Briton to cross the Antarctic unassisted via

4100-641: The British Antarctic Expedition ( Nimrod Expedition ) in a bid to reach the Pole. On 9 January 1909, with three companions, he reached 88°23' S – 112 miles (180 km) from the Pole ;– before being forced to turn back. The first men to reach the Geographic South Pole were the Norwegian Roald Amundsen and his party on 14 December 1911. Amundsen named his camp Polheim and the entire plateau surrounding

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4200-654: The Pole King Haakon VII Vidde in honour of King Haakon VII of Norway . Robert Falcon Scott returned to Antarctica with his second expedition, the Terra Nova Expedition , initially unaware of Amundsen's secretive expedition. Scott and four other men reached the South Pole on 17 January 1912, thirty-four days after Amundsen. On the return trip, Scott and his four companions all died of starvation and extreme cold. In 1914 Ernest Shackleton's Imperial Trans-Antarctic Expedition set out with

4300-515: The Pole are given relative to "grid north", which points northward along the prime meridian . Along tight latitude circles, clockwise is east, and counterclockwise is west, opposite to the North Pole . The Geographic South Pole is presently located on the continent of Antarctica , although this has not been the case for all of Earth's history because of continental drift . It sits atop a featureless, barren, windswept and icy plateau at an altitude of 2,835 m (9,301 ft) above sea level, and

4400-477: The Pole, followed by a short quotation from each man, and gives the elevation as "9,301 FT. ". A new marker stake is designed and fabricated each year by staff at the site. The Ceremonial South Pole is an area set aside for photo opportunities at the South Pole Station . It is located some meters from the Geographic South Pole, and consists of a metallic sphere on a short barber pole, surrounded by

4500-704: The South Pole, when a party led by Admiral George J. Dufek of the US Navy landed there in an R4D-5L Skytrain ( C-47 Skytrain ) aircraft. The US Amundsen–Scott South Pole Station was established by air over 1956–1957 for the International Geophysical Year and has been continuously staffed since then by research and support personnel. After Amundsen and Scott, the next people to reach the South Pole overland (albeit with some air support) were Edmund Hillary (4 January 1958) and Vivian Fuchs (19 January 1958) and their respective parties, during

4600-437: The South Pole. Subsequent to the establishment, in 1987, of the logistic support base at Patriot Hills Base Camp , the South Pole became more accessible to non-government expeditions. On 30 December 1989, Arved Fuchs and Reinhold Messner were the first to traverse Antarctica via the South Pole without animal or motorized help, using only skis and the help of wind. Two women, Victoria E. Murden and Shirley Metz, reached

4700-511: The Sun at the zenith depends on the distance to the Sun and thus on the time of year. It is about 3.3% higher than average in January and 3.3% lower in July (see below). If the extraterrestrial solar radiation is 1,367 watts per square meter (the value when the Earth–Sun distance is 1 astronomical unit ), then the direct sunlight at Earth's surface when the Sun is at the zenith is about 1,050 W/m, but

4800-487: The accumulation of snow amounts to about 7 cm (2.8 in) per year. The former dome seen in pictures of the Amundsen–Scott station is partially buried due to snow storms, and the entrance to the dome had to be regularly bulldozed to uncover it. More recent buildings are raised on stilts so that the snow does not build up against their sides. In most places on Earth, local time is determined by longitude , such that

4900-494: The aphelion (1.01671033 AU) squared should be approximately 0.935338. The solar illuminance constant ( E sc ), is equal to 128×10  lux . The direct normal illuminance ( E dn ), corrected for the attenuating effects of the atmosphere is given by: where c is the atmospheric extinction and m is the relative optical airmass . The atmospheric extinction brings the number of lux down to around 100,000 lux. The total amount of energy received at ground level from

5000-415: The autotrophs are then broken down, releasing stored solar energy, and giving the heterotroph the energy required for survival. This process is known as cellular respiration . In prehistory , humans began to further extend this process by putting plant and animal materials to other uses. They used animal skins for warmth, for example, or wooden weapons to hunt. These skills allowed humans to harvest more of

5100-467: The average temperature remains steady at around −60 °C (−76 °F). The highest temperature ever recorded at the Amundsen–Scott South Pole Station was −12.3 °C (9.9 °F) on Christmas Day, 2011, and the lowest was −82.8 °C (−117.0 °F) on 23 June 1982 (for comparison, the lowest temperature directly recorded anywhere on earth was −89.2 °C (−128.6 °F) at Vostok Station on 21 July 1983, though −93.2 °C (−135.8 °F)

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5200-442: The body. Click on icon in lower right corner to open. Click on genes, proteins and metabolites below to link to respective articles. 7-Dehydrocholesterol is the precursor of cholecalciferol. Within the epidermal layer of skin, 7-dehydrocholesterol undergoes an electrocyclic reaction as a result of UVB light at wavelengths between 290 and 310 nm , with peak synthesis occurring at 293 nm . This results in

5300-422: The brightness of sunlight, many people wear sunglasses . Cars , many helmets and caps are equipped with visors to block the Sun from direct vision when the Sun is at a low angle. Sunshine is often blocked from entering buildings through the use of walls , window blinds , awnings , shutters , curtains , or nearby shade trees . Sunshine exposure is needed biologically for the production of Vitamin D in

5400-445: The change in solar energy in summer and winter. For example, at latitudes of 65 degrees, this can vary by more than 25% as a result of Earth's orbital variation. Because changes in winter and summer tend to offset, the change in the annual average insolation at any given location is near zero, but the redistribution of energy between summer and winter does strongly affect the intensity of seasonal cycles. Such changes associated with

5500-574: The control of these pests. The mechanism of high dose cholecalciferol is that it can produce " hypercalcemia , which results in systemic calcification of soft tissue, leading to kidney failure , cardiac abnormalities, hypertension , CNS depression, and GI upset. Signs generally develop within 18–36 h of ingestion and can include depression, loss of appetite , polyuria , and polydipsia ." High-dose cholecalciferol will tend to rapidly accumulate in adipose tissue yet release more slowly which will tend to delay time of death for several days from

5600-443: The direct radiation is not blocked by clouds, it is experienced as sunshine . The warming of the ground (and other objects) depends on the absorption of the electromagnetic radiation in the form of heat . The amount of radiation intercepted by a planetary body varies inversely with the square of the distance between the star and the planet. Earth's orbit and obliquity change with time (over thousands of years), sometimes forming

5700-499: The elevation difference and for being in the middle of a continent. The North Pole is a few feet from sea level in the middle of an ocean. In midsummer, as the sun reaches its maximum elevation of about 23.5 degrees, high temperatures at the South Pole in January average at −25.9 °C (−15 °F). As the six-month "day" wears on and the sun gets lower, temperatures drop as well: they reach −55 °C (−67 °F) around sunset (late March) and sunrise (late September). In midwinter,

5800-566: The extra UV consisting of biologically damaging short-wave ultraviolet. Direct sunlight has a luminous efficacy of about 93  lumens per watt of radiant flux . This is higher than the efficacy (of source) of artificial lighting other than LEDs , which means using sunlight for illumination heats up a room less than fluorescent or incandescent lighting. Multiplying the figure of 1,050 watts per square meter by 93 lumens per watt indicates that bright sunlight provides an illuminance of approximately 98,000 lux ( lumens per square meter) on

5900-475: The flags of the original Antarctic Treaty signatory states . The tent was erected by the Norwegian expedition led by Roald Amundsen on its arrival on 14 December 1911. It is currently buried beneath the snow and ice in the vicinity of the Pole. It has been designated a Historic Site or Monument (HSM 80), following a proposal by Norway to the Antarctic Treaty Consultative Meeting . The precise location of

6000-461: The goal of crossing Antarctica via the South Pole, but his ship, the Endurance , was frozen in pack ice and sank 11 months later. The overland journey was never made. US Admiral Richard Evelyn Byrd , with the assistance of his first pilot Bernt Balchen , became the first person to fly over the South Pole on 29 November 1929. It was not until 31 October 1956 that humans once again set foot at

6100-485: The incidence of colorectal cancer with minimal risk. Also a 2008 study published in Cancer Research has shown the addition of vitamin D 3 (along with calcium) to the diet of some mice fed a regimen similar in nutritional content to a new Western diet with 1000 IU cholecalciferol per day prevented colon cancer development. In humans, with 400 IU daily, there was no effect of cholecalciferol supplements on

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6200-434: The integration over the orbital period (also invariant) is a constant. If we assume the solar radiation power  P as a constant over time and the solar irradiation given by the inverse-square law , we obtain also the average insolation as a constant. However, the seasonal and latitudinal distribution and intensity of solar radiation received at Earth's surface does vary. The effect of Sun angle on climate results in

6300-405: The intensity of sunlight using a sunshine recorder , pyranometer , or pyrheliometer . To calculate the amount of sunlight reaching the ground, both the eccentricity of Earth's elliptic orbit and the attenuation by Earth's atmosphere have to be taken into account. The extraterrestrial solar illuminance ( E ext ), corrected for the elliptic orbit by using the day number of the year (dn),

6400-472: The kidney through the action of CYP27B1 to convert 25-OH vitamin D 3 into 1,25-dihydroxycholecalciferol ( calcitriol , 1,25-(OH) 2 vitamin D 3 ). All these metabolites are bound in blood to the vitamin D-binding protein . The action of calcitriol is mediated by the vitamin D receptor , a nuclear receptor which regulates the synthesis of hundreds of proteins and is present in virtually every cell in

6500-456: The light within a specific sensitivity range. Many animals (including humans) have a sensitivity range of approximately 400–700 nm, and given optimal conditions the absorption and scattering by Earth's atmosphere produces illumination that approximates an equal-energy illuminant for most of this range. The useful range for color vision in humans, for example, is approximately 450–650 nm. Aside from effects that arise at sunset and sunrise,

6600-462: The only listed carcinogens that are known to have health benefits, and a number of public health organizations state that there needs to be a balance between the risks of having too much sunlight or too little. There is a general consensus that sunburn should always be avoided. Epidemiological data shows that people who have more exposure to sunlight have less high blood pressure and cardiovascular-related mortality. While sunlight (and its UV rays) are

6700-463: The opening of the vitamin precursor B-ring through a conrotatory pathway making previtamin D 3 (pre-cholecalciferol). In a process which is independent of UV light, the pre-cholecalciferol then undergoes a [1,7] antarafacial sigmatropic rearrangement and therein finally isomerizes to form vitamin D 3 . The active UVB wavelengths are little present in sunlight, and sufficient amounts of cholecalciferol can be produced with moderate exposure of

6800-512: The opposite side of Earth from the North Pole , at a distance of 20,004 km (12,430 miles) in all directions. It is one of the two points where Earth's axis of rotation intersects its surface. Situated on the continent of Antarctica , it is the site of the United States Amundsen–Scott South Pole Station , which was established in 1956 and has been permanently staffed since that year. The Geographic South Pole

6900-406: The past 400 years or cosmogenic radionuclides for going back 10,000 years. Such reconstructions have been done. These studies show that in addition to the solar irradiance variation with the solar cycle (the (Schwabe) cycle), the solar activity varies with longer cycles, such as the proposed 88 year (Gleisberg cycle), 208 year (DeVries cycle) and 1,000 year (Eddy cycle). The solar constant

7000-454: The pole by land on 17 January 1989. The fastest unsupported journey to the Geographic South Pole from the ocean is 24 days and one hour from Hercules Inlet and was set in 2011 by Norwegian adventurer Christian Eide, who beat the previous solo record set in 2009 by American Todd Carmichael of 39 days and seven hours, and the previous group record also set in 2009 of 33 days and 23 hours. The fastest solo, unsupported and unassisted trek to

7100-400: The principal source of illumination is sunlight as mediated by the atmosphere. While the color of the sky is usually determined by Rayleigh scattering , an exception occurs at sunset and twilight. "Preferential absorption of sunlight by ozone over long horizon paths gives the zenith sky its blueness when the sun is near the horizon". The Sun may be said to illuminate , which is a measure of

7200-438: The radiance at the center of the sun's disk is somewhat higher than the average over the whole disk due to limb darkening .) Multiplying this by π gives an upper limit to the irradiance which can be focused on a surface using mirrors: 48.5 MW/m. The spectrum of the Sun's solar radiation can be compared to that of a black body with a temperature of about 5,800  K (see graph). The Sun emits EM radiation across most of

7300-442: The redistribution of solar energy are considered a likely cause for the coming and going of recent ice ages (see: Milankovitch cycles ). Space-based observations of solar irradiance started in 1978. These measurements show that the solar constant is not constant. It varies on many time scales, including the 11-year sunspot solar cycle. When going further back in time, one has to rely on irradiance reconstructions, using sunspots for

7400-573: The relevant satellite observations indicate a value closer to 1,361 W/m is more realistic. Since 1978, a series of overlapping NASA and ESA satellite experiments have measured total solar irradiance (TSI) – the amount of solar radiation received at the top of Earth's atmosphere – as 1.365 kilo⁠watts per square meter (kW/m). TSI observations continue with the ACRIMSAT /ACRIM3, SOHO /VIRGO and SORCE /TIM satellite experiments. Observations have revealed variation of TSI on many timescales, including

7500-499: The remnants of ancient plant and animal matter, formed using energy from sunlight and then trapped within Earth for millions of years. The effect of sunlight is relevant to painting , evidenced for instance in works of Édouard Manet and Claude Monet on outdoor scenes and landscapes. Many people find direct sunlight to be too bright for comfort; indeed, looking directly at the Sun can cause long-term vision damage. To compensate for

7600-461: The risk of colorectal cancer. Supplements are not recommended for prevention of cancer as any effects of cholecalciferol are very small. Although correlations exist between low levels of blood serum cholecalciferol and higher rates of various cancers, multiple sclerosis , tuberculosis , heart disease, and diabetes, the consensus is that supplementing levels is not beneficial. It is thought that tuberculosis may result in lower levels. It, however,

7700-473: The same source reports that use of cholecalciferol in rodenticides may still pose a significant hazard to other animals, such as dogs and cats, when rodenticide bait or other forms of cholecalciferol are directly ingested. South Pole The South Pole , also known as the Geographic South Pole or Terrestrial South Pole , is the southernmost point on Earth and lies antipodally on

7800-486: The skin, a vital compound needed to make strong bone and muscle in the body. In many world religions, such as Hinduism , the Sun is considered to be a god , as it is the source of life and energy on Earth. The Sun was also considered to be a god in Ancient Egypt . Sunbathing is a popular leisure activity in which a person sits or lies in direct sunshine. People often sunbathe in comfortable places where there

7900-411: The skin, depending on the strength of the sun. Time of day, season, latitude, and altitude affect the strength of the sun, and pollution, cloud cover or glass all reduce the amount of UVB exposure. Exposure of face, arms and legs, averaging 5–30  minutes twice per week, may be sufficient, but the darker the skin, and the weaker the sunlight, the more minutes of exposure are needed. Vitamin D overdose

8000-496: The skin. Supplements are recommended for these groups of people. The Institute of Medicine in 2010 recommended a maximum uptake of vitamin D of 4000 IU/d , finding that the dose for lowest observed adverse effect level is 40,000 IU daily for at least 12 weeks, and that there was a single case of toxicity above 10 000  IU after more than seven years of daily intake; this case of toxicity occurred in circumstances that have led other researchers to dispute whether it

8100-445: The solar atmosphere, but this does not explain these findings. The only direct signature of the nuclear processes in the core of the Sun is via the very weakly interacting neutrinos . Although the solar corona is a source of extreme ultraviolet and X-ray radiation, these rays make up only a very small amount of the power output of the Sun (see spectrum at right). The spectrum of nearly all solar electromagnetic radiation striking

8200-490: The solar light it receives. The actual illumination of the surface is about 14,000 lux, comparable to that on Earth "in the daytime with overcast clouds". Sunlight on Mars would be more or less like daylight on Earth during a slightly overcast day, and, as can be seen in the pictures taken by the rovers, there is enough diffuse sky radiation that shadows would not seem particularly dark. Thus, it would give perceptions and "feel" very much like Earth daylight. The spectrum on

8300-590: The solar magnetic cycle and many shorter periodic cycles. TSI provides the energy that drives Earth's climate, so continuation of the TSI time-series database is critical to understanding the role of solar variability in climate change. Since 2003, the SORCE Spectral Irradiance Monitor (SIM) has monitored Spectral solar irradiance (SSI) – the spectral distribution of the TSI. Data indicate that SSI at UV (ultraviolet) wavelength corresponds in

8400-501: The south pole by a female was performed by Hannah McKeand from the UK in 2006. She made the journey in 39 days 9 hours 33 minutes. She started on 19 November 2006 and finished on 28 December 2006. In the 2011–12 summer, separate expeditions by Norwegian Aleksander Gamme and Australians James Castrission and Justin Jones jointly claimed the first unsupported trek without dogs or kites from

8500-434: The south pole, and the second person to make the journey in 56 days. On 10 January 2020, Mollie Hughes became the youngest person to ski to the pole, aged 29. During winter (May through August), the South Pole receives no sunlight at all, and is completely dark apart from moonlight. In summer (November through February), the sun is continuously above the horizon and appears to move in a counter-clockwise circle. However, it

8600-406: The spectral composition changes primarily in respect to how directly sunlight is able to illuminate. When illumination is indirect, Rayleigh scattering in the upper atmosphere will lead blue wavelengths to dominate. Water vapour in the lower atmosphere produces further scattering and ozone, dust and water particles will also absorb particular wavelengths. The existence of nearly all life on Earth

8700-605: The sunlight than was possible through glycolysis alone, and human population began to grow. During the Neolithic Revolution , the domestication of plants and animals further increased human access to solar energy. Fields devoted to crops were enriched by inedible plant matter, providing sugars and nutrients for future harvests. Animals that had previously provided humans with only meat and tools once they were killed were now used for labour throughout their lives, fueled by grasses inedible to humans. Fossil fuels are

8800-486: The surface is slightly redder than that on Earth, due to scattering by reddish dust in the Martian atmosphere. For comparison, sunlight on Saturn is slightly brighter than Earth sunlight at the average sunset or sunrise. Even on Pluto, the sunlight would still be bright enough to almost match the average living room. To see sunlight as dim as full moonlight on Earth, a distance of about 500 AU (~69  light-hours )

8900-451: The surface. Sunlight is a key factor in photosynthesis , the process used by plants and other autotrophic organisms to convert light energy , normally from the Sun, into chemical energy that can be used to synthesize carbohydrates and fuel the organisms' activities. Daylighting is the natural lighting of interior spaces by admitting sunlight. Solar irradiance is the solar energy available from sunlight. Researchers can measure

9000-590: The tent is unknown, but based on calculations of the rate of movement of the ice and the accumulation of snow, it is believed, as of 2010, to lie between 1.8 and 2.5 km (1.1 and 1.5 miles) from the Pole at a depth of 17 m (56 ft) below the present surface. A flagpole erected at the South Geographical Pole in December 1965 by the First Argentine Overland Polar Expedition has been designated

9100-441: The time of day is more-or-less synchronised to the perceived position of the Sun in the sky (for example, at midday the Sun is roughly perceived to be at its highest). This line of reasoning fails at the South Pole, where the Sun is seen to rise and set only once per year with solar elevation varying only with day of the year, not time of day. There is no a priori reason for placing the South Pole in any particular time zone, but as

9200-519: The time that high-dose bait is introduced. In New Zealand, possums have become a significant pest animal. For possum control, cholecalciferol has been used as the active ingredient in lethal baits. The LD 50 is 16.8 mg/kg, but only 9.8 mg/kg if calcium carbonate is added to the bait. Kidneys and heart are target organs. LD 50 of 4.4 mg/kg has been reported in rabbits, with lethality to almost all rabbits ingesting doses greater than 15 mg/kg. Toxicity has been reported across

9300-472: The timing of melatonin synthesis, maintenance of normal circadian rhythms , and reduced risk of seasonal affective disorder . Long-term sunlight exposure is known to be associated with the development of skin cancer , skin aging , immune suppression , and eye diseases such as cataracts and macular degeneration . Short-term overexposure is the cause of sunburn , snow blindness , and solar retinopathy . UV rays, and therefore sunlight and sunlamps, are

9400-414: The total amount (direct and indirect from the atmosphere) hitting the ground is around 1,120 W/m. In terms of energy, sunlight at Earth's surface is around 52 to 55 percent infrared (above 700 nm ), 42 to 43 percent visible (400 to 700 nm), and 3 to 5 percent ultraviolet (below 400 nm). At the top of the atmosphere, sunlight is about 30% more intense, having about 8% ultraviolet (UV), with most of

9500-430: The two forms, with evidence usually favoring cholecalciferol in raising levels in blood, although more research is needed. A much less common use of cholecalciferol therapy in rickets utilizes a single large dose and has been called stoss therapy. Treatment is given either orally or by intramuscular injection of 300 000  IU ( 7500 μg ) to 500 000  IU ( 12 500  μg  = 12.5 mg ), in

9600-533: The web. Different bodies of the Solar System receive light of an intensity inversely proportional to the square of their distance from Sun. A table comparing the amount of solar radiation received by each planet in the Solar System at the top of its atmosphere: The actual brightness of sunlight that would be observed at the surface also depends on the presence and composition of an atmosphere . For example, Venus's thick atmosphere reflects more than 60% of

9700-671: Was first described in 1936. It is on the World Health Organization's List of Essential Medicines . In 2022, it was the 62nd most commonly prescribed medication in the United States, with more than 10   million prescriptions. Cholecalciferol is available as a generic medication . Cholecalciferol (vitamin D3) appears to stimulate the body's interferon type I signaling system that protects against bacteria and viruses, unlike vitamin D 2 . Cholecalciferol

9800-399: Was found to be 2.4 times more efficient in producing vitamin D3 than the sun in less than 1 ⁄ 60 the time. ( https://pubmed.ncbi.nlm.nih.gov/28904394/ ). Whether cholecalciferol and all forms of vitamin D are by definition " vitamins " can be disputed, since the definition of vitamins includes that the substance cannot be synthesized by the body and must be ingested. Cholecalciferol

9900-529: Was measured indirectly by satellite in East Antarctica between Dome A and Dome F in August 2010 ). Mean annual temperature at the South Pole is –49.5 °C (–57.1 °F). The South Pole has an ice cap climate ( Köppen climate classification EF ). It resembles a desert, receiving very little precipitation. Air humidity is near zero. However, high winds can cause the blowing of snowfall, and

10000-484: Was unsuccessful. British explorer Robert Falcon Scott on the Discovery Expedition of 1901–1904 was the first to attempt to find a route from the Antarctic coastline to the South Pole. Scott, accompanied by Ernest Shackleton and Edward Wilson , set out with the aim of travelling as far south as possible, and on 31 December 1902, reached 82°16′ S. Shackleton later returned to Antarctica as leader of

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