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112-558: Concordia Research Station , which opened in 2005, is a French–Italian research facility that was built 3,233 m (10,607 ft) above sea level at a location called Dome C on the Antarctic Plateau , Antarctica . It is located 1,100 km (680 mi) inland from the French research station at Dumont D'Urville , 1,100 km (680 mi) inland from Australia's Casey Station and 1,200 km (750 mi) inland from

224-474: A 150W RF output and a delta loop antenna located a few hundreds of meters away from the station. The analemma (path that the sun follows in the sky if photographed at precisely the same time every week through the course of a year) was imaged for the first time ever in Antarctica by Adrianos Golemis during the 10th winterover mission at Concordia Station (2013–2014). The resulting composite exposure image

336-494: A French-Italian team established a summer camp at Dome C. The two main objectives of the camp were the provision of logistical support for the European Project for Ice Coring in Antarctica (EPICA) and the construction of a permanent research station. The new all-year facility, Concordia Station , became operational in 2005. The Advisory Committee on Antarctic Names (US-ACAN) considers "Dome Charlie" to be superior to

448-483: A central subject for astronomical research since antiquity . The Sun orbits the Galactic Center at a distance of 24,000 to 28,000 light-years . From Earth, it is 1  astronomical unit ( 1.496 × 10  km ) or about 8 light-minutes away. Its diameter is about 1,391,400 km ( 864,600 mi ), 109 times that of Earth. Its mass is about 330,000 times that of Earth, making up about 99.86% of

560-564: A distance of one astronomical unit (AU) from the Sun (that is, at or near Earth's orbit). Sunlight on the surface of Earth is attenuated by Earth's atmosphere , so that less power arrives at the surface (closer to 1,000 W/m ) in clear conditions when the Sun is near the zenith . Sunlight at the top of Earth's atmosphere is composed (by total energy) of about 50% infrared light, 40% visible light, and 10% ultraviolet light. The atmosphere filters out over 70% of solar ultraviolet, especially at

672-403: A fairly small amount of power being generated per cubic metre . Theoretical models of the Sun's interior indicate a maximum power density, or energy production, of approximately 276.5 watts per cubic metre at the center of the core, which, according to Karl Kruszelnicki , is about the same power density inside a compost pile . The fusion rate in the core is in a self-correcting equilibrium:

784-414: A few millimeters. Re-emission happens in a random direction and usually at slightly lower energy. With this sequence of emissions and absorptions, it takes a long time for radiation to reach the Sun's surface. Estimates of the photon travel time range between 10,000 and 170,000 years. In contrast, it takes only 2.3 seconds for neutrinos , which account for about 2% of the total energy production of

896-401: A granular appearance called the solar granulation at the smallest scale and supergranulation at larger scales. Turbulent convection in this outer part of the solar interior sustains "small-scale" dynamo action over the near-surface volume of the Sun. The Sun's thermal columns are Bénard cells and take the shape of roughly hexagonal prisms. The visible surface of the Sun, the photosphere,

1008-675: A great opportunity to benefit from an access to the best astronomical site on Earth –Dome C–. Indeed, Chadid, Vernin, Preston et al. implement, for the first time from the ground, a new way to study the stellar oscillations , pulsations and their evolutionary properties with long uninterrupted and continuous precision observations over 150 days, and without the regular interruptions imposed by the Earth rotation . PAIX achieves astrophysical UBVRI bands time-series measurements of stellar physics fields, challenging photometry from Space . The Antarctic Search for Transiting ExoPlanets (ASTEP) programme

1120-464: A high percentage of cloud -free time, low atmospheric aerosol and dust content, and freedom from light pollution and background light other than auroras and moonlight. This location was a serious candidate for the ESO 's E-ELT project. However, sky coverage is less than at lower latitude locations as northern celestial hemisphere objects never rise or are too low above the horizon. The Proceedings of

1232-491: A maximum summer population of 18, was operated and maintained by four employees of ITT Antarctic Services and one US Navy medical corpsman. When the camp was shut down for the season in about January, 1980, it was left mostly intact, with a radio-isotope powered remote weather station operational. In 1992, France decided to build a new station on the Antarctic Plateau. The program was later joined by Italy. In 1996,

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1344-520: A period known as the Maunder minimum . This coincided in time with the era of the Little Ice Age , when Europe experienced unusually cold temperatures. Earlier extended minima have been discovered through analysis of tree rings and appear to have coincided with lower-than-average global temperatures. The temperature of the photosphere is approximately 6,000 K, whereas the temperature of

1456-485: A phenomenon described by Hale's law . During the solar cycle's declining phase, energy shifts from the internal toroidal magnetic field to the external poloidal field, and sunspots diminish in number and size. At solar-cycle minimum, the toroidal field is, correspondingly, at minimum strength, sunspots are relatively rare, and the poloidal field is at its maximum strength. With the rise of the next 11-year sunspot cycle, differential rotation shifts magnetic energy back from

1568-473: A result, the outward-flowing solar wind stretches the interplanetary magnetic field outward, forcing it into a roughly radial structure. For a simple dipolar solar magnetic field, with opposite hemispherical polarities on either side of the solar magnetic equator, a thin current sheet is formed in the solar wind. At great distances, the rotation of the Sun twists the dipolar magnetic field and corresponding current sheet into an Archimedean spiral structure called

1680-410: A slightly higher rate of fusion would cause the core to heat up more and expand slightly against the weight of the outer layers, reducing the density and hence the fusion rate and correcting the perturbation ; and a slightly lower rate would cause the core to cool and shrink slightly, increasing the density and increasing the fusion rate and again reverting it to its present rate. The radiative zone

1792-559: A staff of 13 (eleven French and 2 Italians) in February 2005. Most of the cargo is moved to Dome C by traverse (called raid) from Dumont d'Urville Station , covering 1,200 kilometres (750 mi) in 7 to 12 days depending on weather conditions. Station personnel and light cargo arrive by air, landing on a Skiway, using the Twin Otters or Basler BT-67 flying from DDU or Zucchelli Station at 1,200 kilometres (750 mi). Dome C

1904-427: A team of 15 people (nine French, five Italian and one Greek): The tenth wintering took place with a team of 13 people (six French, five Italian, one Russian and one Greek): During the 2014 Antarctic winter Concordia was an active amateur radio station: Paride Legovini operated from there on a weekly basis with call sign IA/IZ3SUS. The HF radio equipment consists in a Rohde & Schwarz XK2100L transceiver with

2016-424: A team of twelve people (eight French, three Italian and one British): This Wintering took place with a team of thirteen (six French, six Italian and one Czech): The seventh wintering took place with a team of 14 people (seven French, six Italian and one British): The eighth wintering took place with a team of 13 people (seven French, four Italian, one Russian and one British): The ninth wintering took place with

2128-425: A team of wintering composed of fourteen people (eight French and six Italian): The average temperature was −65 °C and the minimum temperature recorded was −81.9 °C reached on September 5. The fourth winter took place from 31 January 2008 to 8 November 2008 with a team consisting of thirteen winter-overs (seven French and six Italian): The fifth wintering took place from February 2009 to November 2009 with

2240-406: A transition layer, the tachocline . This is a region where the sharp regime change between the uniform rotation of the radiative zone and the differential rotation of the convection zone results in a large shear between the two—a condition where successive horizontal layers slide past one another. Presently, it is hypothesized that a magnetic dynamo, or solar dynamo , within this layer generates

2352-415: A useful analogue platform for research relevant to space medicine. During the winter, the crew are isolated from the outside world, having no transportation and limited communication for 9 months and live a prolonged period in complete darkness, at an altitude almost equivalent to 4000m at the equator. This creates physiological and psychological strains on the crew. Concordia station is particularly useful for

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2464-433: Is also very dry, with very little precipitation throughout the year. Dome C does not experience the katabatic winds typical for the coastal regions of Antarctica because of its elevated location and its relative distance from the edges of the Antarctic Plateau. Typical wind speed in winter is 2.8 m/s. While the station has been in use for summer campaigns since December 1997, the first winterover (February to October)

2576-546: Is believed that these seabirds have learned to cross the frozen white continent instead of circumnavigating it. Dome C is notable for its potential to be an extremely good astronomical observation site; the transparency of the Antarctic atmosphere allows stars to be observed, even when the Sun is at its highest possible elevation angle of 38°. The good viewing is due to very low infrared sky emission, extremely low humidity ,

2688-643: Is by far the brightest object in the Earth's sky , with an apparent magnitude of −26.74. This is about 13 billion times brighter than the next brightest star, Sirius , which has an apparent magnitude of −1.46. One astronomical unit (about 150 million kilometres; 93 million miles) is defined as the mean distance between the centres of the Sun and the Earth. The instantaneous distance varies by about ± 2.5 million km or 1.55 million miles as Earth moves from perihelion on ~ January 3rd to aphelion on ~ July 4th. At its average distance, light travels from

2800-763: Is composed of two telescopes: a 10 cm refractor installed in 2008, and a 40 cm telescope installed in 2010 and upgraded in 2022. The climate at Dome C where Concordia Station is located is frigid all year round, being one of the coldest places on Earth. It has a polar ice cap climate ( Köppen EF ), with maximums ranging from −24.8 °C (−12.6 °F) in December to −62 °C (−80 °F) in May, mean ranging from −30.4 °C (−22.7 °F) in December to −65.3 °C (−85.5 °F) in May and minimums ranging from −36.1 °C (−33.0 °F) in December to −68.7 °C (−91.7 °F) in May. The annual average air temperature

2912-436: Is defined to begin at the distance where the flow of the solar wind becomes superalfvénic —that is, where the flow becomes faster than the speed of Alfvén waves, at approximately 20 solar radii ( 0.1 AU ). Turbulence and dynamic forces in the heliosphere cannot affect the shape of the solar corona within, because the information can only travel at the speed of Alfvén waves. The solar wind travels outward continuously through

3024-402: Is facilitated by the full ionization of helium in the transition region, which significantly reduces radiative cooling of the plasma. The transition region does not occur at a well-defined altitude, but forms a kind of nimbus around chromospheric features such as spicules and filaments , and is in constant, chaotic motion. The transition region is not easily visible from Earth's surface, but

3136-493: Is one of the coldest places on Earth. Temperatures hardly rise above −25 °C (−13 °F) in summer and can fall below −80 °C (−112 °F) in winter. The annual average air temperature is −54.5 °C (−66.1 °F). Humidity is low and it is also very dry, with very little or no precipitation throughout the year. Dome C does not experience the katabatic winds typical of the coastal regions of Antarctica because of its elevated location and its relative distance from

3248-409: Is only 84% of what it was in the protostellar phase (before nuclear fusion in the core started). In the future, helium will continue to accumulate in the core, and in about 5 billion years this gradual build-up will eventually cause the Sun to exit the main sequence and become a red giant . The chemical composition of the photosphere is normally considered representative of the composition of

3360-441: Is readily observable from space by instruments sensitive to extreme ultraviolet . The corona is the next layer of the Sun. The low corona, near the surface of the Sun, has a particle density around 10  m to 10  m . The average temperature of the corona and solar wind is about 1,000,000–2,000,000 K; however, in the hottest regions it is 8,000,000–20,000,000 K. Although no complete theory yet exists to account for

3472-596: Is significantly worse than most major observatory sites, but similar to other observatories in Antarctica. However, Lawrence et al. consider other features of the site and conclude that "Dome C is the best ground-based site to develop a new astronomical observatory". Note however that this was written before whole-atmospheric seeing measurements had been made at Dome C. Thanks to the Single Star Scidar SSS, Vernin, Chadid and Aristidi et al. and Giordano, Vernin and Chadid et al. finally demonstrated that most of

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3584-619: Is situated on top of the Antarctic Plateau. No animals or plants live at a distance of more than a few tens of kilometers from the Southern Ocean . However, south polar skuas have been spotted overflying the station, 1,200 km away from their nearest food sources. It is believed that these birds have learned to cross the continent instead of circumnavigating it. Concordia Station shares many stressor characteristics similar to that of long-duration deep-space missions, in particular extreme isolation and confinement, and therefore serves as

3696-410: Is strongly attenuated by Earth's ozone layer , so that the amount of UV varies greatly with latitude and has been partially responsible for many biological adaptations, including variations in human skin color . High-energy gamma ray photons initially released with fusion reactions in the core are almost immediately absorbed by the solar plasma of the radiative zone, usually after traveling only

3808-483: Is suggested by a high abundance of heavy elements in the Solar System, such as gold and uranium , relative to the abundances of these elements in so-called Population II , heavy-element-poor, stars. The heavy elements could most plausibly have been produced by endothermic nuclear reactions during a supernova, or by transmutation through neutron absorption within a massive second-generation star. The Sun

3920-470: Is tens to hundreds of kilometers thick, and is slightly less opaque than air on Earth. Because the upper part of the photosphere is cooler than the lower part, an image of the Sun appears brighter in the center than on the edge or limb of the solar disk, in a phenomenon known as limb darkening . The spectrum of sunlight has approximately the spectrum of a black-body radiating at 5,772 K (9,930 °F), interspersed with atomic absorption lines from

4032-509: Is the star at the center of the Solar System . It is a massive, nearly perfect sphere of hot plasma , heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light and infrared radiation with 10% at ultraviolet energies. It is by far the most important source of energy for life on Earth . The Sun has been an object of veneration in many cultures. It has been

4144-437: Is the layer below which the Sun becomes opaque to visible light. Photons produced in this layer escape the Sun through the transparent solar atmosphere above it and become solar radiation, sunlight. The change in opacity is due to the decreasing amount of H ions , which absorb visible light easily. Conversely, the visible light perceived is produced as electrons react with hydrogen atoms to produce H ions. The photosphere

4256-424: Is the most prominent variation in which the number and size of sunspots waxes and wanes. The solar magnetic field extends well beyond the Sun itself. The electrically conducting solar wind plasma carries the Sun's magnetic field into space, forming what is called the interplanetary magnetic field . In an approximation known as ideal magnetohydrodynamics , plasma particles only move along magnetic field lines. As

4368-531: Is the only region of the Sun that produces an appreciable amount of thermal energy through fusion; 99% of the Sun's power is generated in the innermost 24% of its radius, and almost no fusion occurs beyond 30% of the radius. The rest of the Sun is heated by this energy as it is transferred outward through many successive layers, finally to the solar photosphere where it escapes into space through radiation (photons) or advection (massive particles). The proton–proton chain occurs around 9.2 × 10 times each second in

4480-420: Is the thickest layer of the Sun, at 0.45 solar radii. From the core out to about 0.7 solar radii , thermal radiation is the primary means of energy transfer. The temperature drops from approximately 7 million to 2 million kelvins with increasing distance from the core. This temperature gradient is less than the value of the adiabatic lapse rate and hence cannot drive convection, which explains why

4592-538: Is ultimately related to the word for sun in other branches of the Indo-European language family, though in most cases a nominative stem with an l is found, rather than the genitive stem in n , as for example in Latin sōl , ancient Greek ἥλιος ( hēlios ), Welsh haul and Czech slunce , as well as (with *l > r ) Sanskrit स्वर् ( svár ) and Persian خور ( xvar ). Indeed,

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4704-402: Is wave heating, in which sound, gravitational or magnetohydrodynamic waves are produced by turbulence in the convection zone. These waves travel upward and dissipate in the corona, depositing their energy in the ambient matter in the form of heat. The other is magnetic heating, in which magnetic energy is continuously built up by photospheric motion and released through magnetic reconnection in

4816-514: Is −54.5 °C (−66.1 °F). The station has never recorded a temperature above freezing; the warmest temperature recorded was −5.4 °C (22.3 °F) in January. Temperatures can fall below −80 °C (−112 °F) in winter, and the coldest recorded temperature was −84.6 °C (−120.3 °F) in August 2010; one of the coldest temperatures ever recorded on Earth. Humidity is low and it

4928-547: The Alfvén surface , the boundary separating the corona from the solar wind, defined as where the coronal plasma's Alfvén speed and the large-scale solar wind speed are equal. During the flyby, Parker Solar Probe passed into and out of the corona several times. This proved the predictions that the Alfvén critical surface is not shaped like a smooth ball, but has spikes and valleys that wrinkle its surface. The Sun emits light across

5040-570: The Amundsen–Scott South Pole Station (U.S.) at the Geographic South Pole . It is jointly operated by scientists from France and Italy and regularly hosts ESA scientists. In 1992, France built a new station on the Antarctic Plateau. The program was later joined by Italy in 1993. In 1995, Pr. Jean Vernin from University of Nice Sophia-Antipolis and Pr. Giorgio Dall'Oglio from University of Rome performed

5152-524: The Parker spiral . Sunspots are visible as dark patches on the Sun's photosphere and correspond to concentrations of magnetic field where convective transport of heat is inhibited from the solar interior to the surface. As a result, sunspots are slightly cooler than the surrounding photosphere, so they appear dark. At a typical solar minimum , few sunspots are visible, and occasionally none can be seen at all. Those that do appear are at high solar latitudes. As

5264-455: The U.S. Navy established field camps on Dome Charlie to recover the aircraft. Following major structural repairs and replacement of engines in the field, the three LC-130s were flown to McMurdo Station on December 26, 1975, January 14, 1976, and December 25 (Christmas Day), 1976. From November 1977 to March 1978 a French party of 13 settled down in the existing camp left by the aircraft rescuers. They brought several tons of equipment—thanks to

5376-410: The corona , and the heliosphere . The coolest layer of the Sun is a temperature minimum region extending to about 500 km above the photosphere, and has a temperature of about 4,100  K . This part of the Sun is cool enough to allow for the existence of simple molecules such as carbon monoxide and water. The chromosphere, transition region, and corona are much hotter than the surface of

5488-531: The gravitational collapse of matter within a region of a large molecular cloud . Most of this matter gathered in the center, whereas the rest flattened into an orbiting disk that became the Solar System . The central mass became so hot and dense that it eventually initiated nuclear fusion in its core . Every second, the Sun's core fuses about 600 billion kilograms (kg) of hydrogen into helium and converts 4 billion kg of matter into energy . About 4 to 7 billion years from now, when hydrogen fusion in

5600-614: The l -stem survived in Proto-Germanic as well, as * sōwelan , which gave rise to Gothic sauil (alongside sunnō ) and Old Norse prosaic sól (alongside poetic sunna ), and through it the words for sun in the modern Scandinavian languages: Swedish and Danish sol , Icelandic sól , etc. The principal adjectives for the Sun in English are sunny for sunlight and, in technical contexts, solar ( / ˈ s oʊ l ər / ), from Latin sol . From

5712-428: The photosphere . For the purpose of measurement, the Sun's radius is considered to be the distance from its center to the edge of the photosphere, the apparent visible surface of the Sun. By this measure, the Sun is a near-perfect sphere with an oblateness estimated at 9 millionths, which means that its polar diameter differs from its equatorial diameter by only 10 kilometers (6.2 mi). The tidal effect of

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5824-444: The visible spectrum , so its color is white , with a CIE color-space index near (0.3, 0.3), when viewed from space or when the Sun is high in the sky. The Solar radiance per wavelength peaks in the green portion of the spectrum when viewed from space. When the Sun is very low in the sky, atmospheric scattering renders the Sun yellow, red, orange, or magenta, and in rare occasions even green or blue . Some cultures mentally picture

5936-460: The 1970s, Dome C was the site of ice core drilling by field teams of several nations. It was called Dome Charlie ( NATO Phonetic Alphabet code for the letter C ) by the U.S. Naval Support Force , Antarctica, and its Squadron VXE-6 , which provided logistical support to the field teams. In January and November 1975, three LC-130 Hercules aircraft suffered severe damage during attempted takeoffs from Dome Charlie. In November 1975 and November 1976,

6048-522: The 1990s, Dome C was chosen for deep ice core drilling by the European Project for Ice Coring in Antarctica (EPICA). Drilling at Dome C began in 1996 and was completed on December 21, 2004, reaching a drilling depth of 3270.2 m, 5 m above bedrock. The age of the oldest recovered ice is estimated to be ca. 900,000 years. Concordia Station has been identified as a suitable location for extremely accurate astronomical observations. The transparency of

6160-433: The Antarctic atmosphere permits the observation of stars even when the sun is at an elevation angle of 38°. Other advantages include the very low infrared sky emission, the high percentage of cloud -free time and the low aerosol and dust content of the atmosphere . The median seeing measured with a DIMM Differential Image Motion Monitor placed on top of an 8.5 m high tower is 1.3 ± 0.8 arcseconds . This

6272-650: The Astronomical Society of the Pacific discuss the suitability of the site for astronomy in terms of the seeing . They determined the median seeing (measured with a Differential Image Motion Monitor placed on top of an 8.5-metre-high (28 ft) tower) to be 1.3±0.8 arcseconds . This is significantly worse than most major observatory sites, but similar to other observatories in Antarctica . However, they found (using balloons ) that 87% of turbulence

6384-528: The Concordia crew and Astronauts have to face, they both live in isolation and confinement, in different atmospheric pressure conditions, with an abnormal day/night cycle plus several effects on their everyday life, such as sleep difficulties. Obviously the above parameters influence not only physiology but also psychology. The European Space Agency ( ESA ) hires a Medical Doctor each year to winterover at Concordia Station and facilitate biomedical experiments on

6496-465: The Greek helios comes the rare adjective heliac ( / ˈ h iː l i æ k / ). In English, the Greek and Latin words occur in poetry as personifications of the Sun, Helios ( / ˈ h iː l i ə s / ) and Sol ( / ˈ s ɒ l / ), while in science fiction Sol may be used to distinguish the Sun from other stars. The term sol with a lowercase s is used by planetary astronomers for

6608-641: The Italian Zucchelli Station at Terra Nova Bay . Russia's Vostok Station is 560 km (350 mi) away. The Geographic South Pole is 1,670 km (1,040 mi) away. The facility is also located within Australia's claim on Antarctica, the Australian Antarctic Territory . Concordia Station is the third permanent, all-year research station on the Antarctic Plateau besides Vostok Station (Russian) and

6720-446: The Solar System . Long-term secular change in sunspot number is thought, by some scientists, to be correlated with long-term change in solar irradiance, which, in turn, might influence Earth's long-term climate. The solar cycle influences space weather conditions, including those surrounding Earth. For example, in the 17th century, the solar cycle appeared to have stopped entirely for several decades; few sunspots were observed during

6832-443: The Sun as yellow and some even red; the cultural reasons for this are debated. The Sun is classed as a G2 star, meaning it is a G-type star , with 2 indicating its surface temperature is in the second range of the G class. The solar constant is the amount of power that the Sun deposits per unit area that is directly exposed to sunlight. The solar constant is equal to approximately 1,368 W/m (watts per square meter) at

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6944-424: The Sun extends from the center to about 20–25% of the solar radius. It has a density of up to 150 g/cm (about 150 times the density of water) and a temperature of close to 15.7 million kelvin (K). By contrast, the Sun's surface temperature is about 5800 K . Recent analysis of SOHO mission data favors the idea that the core is rotating faster than the radiative zone outside it. Through most of

7056-688: The Sun will shed its outer layers and become a dense type of cooling star (a white dwarf ), and no longer produce energy by fusion, but will still glow and give off heat from its previous fusion for perhaps trillions of years. After that, it is theorized to become a super dense black dwarf , giving off negligible energy. The English word sun developed from Old English sunne . Cognates appear in other Germanic languages , including West Frisian sinne , Dutch zon , Low German Sünn , Standard German Sonne , Bavarian Sunna , Old Norse sunna , and Gothic sunnō . All these words stem from Proto-Germanic * sunnōn . This

7168-413: The Sun's magnetic field . The Sun's convection zone extends from 0.7 solar radii (500,000 km) to near the surface. In this layer, the solar plasma is not dense or hot enough to transfer the heat energy of the interior outward via radiation. Instead, the density of the plasma is low enough to allow convective currents to develop and move the Sun's energy outward towards its surface. Material heated at

7280-398: The Sun's core by radiation rather than by convection (see Radiative zone below), so the fusion products are not lifted outward by heat; they remain in the core, and gradually an inner core of helium has begun to form that cannot be fused because presently the Sun's core is not hot or dense enough to fuse helium. In the current photosphere, the helium fraction is reduced, and the metallicity

7392-426: The Sun's core diminishes to the point where the Sun is no longer in hydrostatic equilibrium , its core will undergo a marked increase in density and temperature which will cause its outer layers to expand, eventually transforming the Sun into a red giant . This process will make the Sun large enough to render Earth uninhabitable approximately five billion years from the present. After the red giant phase, models suggest

7504-403: The Sun's horizon to Earth's horizon in about 8 minutes and 20 seconds, while light from the closest points of the Sun and Earth takes about two seconds less. The energy of this sunlight supports almost all life on Earth by photosynthesis , and drives Earth's climate and weather. The Sun does not have a definite boundary, but its density decreases exponentially with increasing height above

7616-499: The Sun's life, energy has been produced by nuclear fusion in the core region through the proton–proton chain ; this process converts hydrogen into helium. Currently, 0.8% of the energy generated in the Sun comes from another sequence of fusion reactions called the CNO cycle ; the proportion coming from the CNO cycle is expected to increase as the Sun becomes older and more luminous. The core

7728-551: The Sun's life, they account for 74.9% and 23.8%, respectively, of the mass of the Sun in the photosphere. All heavier elements, called metals in astronomy, account for less than 2% of the mass, with oxygen (roughly 1% of the Sun's mass), carbon (0.3%), neon (0.2%), and iron (0.2%) being the most abundant. The Sun's original chemical composition was inherited from the interstellar medium out of which it formed. Originally it would have been about 71.1% hydrogen, 27.4% helium, and 1.5% heavier elements. The hydrogen and most of

7840-438: The Sun, to reach the surface. Because energy transport in the Sun is a process that involves photons in thermodynamic equilibrium with matter , the time scale of energy transport in the Sun is longer, on the order of 30,000,000 years. This is the time it would take the Sun to return to a stable state if the rate of energy generation in its core were suddenly changed. Electron neutrinos are released by fusion reactions in

7952-402: The Sun. The reason is not well understood, but evidence suggests that Alfvén waves may have enough energy to heat the corona. Above the temperature minimum layer is a layer about 2,000 km thick, dominated by a spectrum of emission and absorption lines. It is called the chromosphere from the Greek root chroma , meaning color, because the chromosphere is visible as a colored flash at

8064-678: The VXE-6 airplanes—and achieved the planned ice-coring campaign down to 980 m bringing to surface, and later on in their labs for study, ice samples 45,000 to 50,000 years old. During the Antarctic summer of 1979, the camp was re-occupied by Americans and French, under the auspices of the US Antarctic Research Program, sponsored by the National Science Foundation. Deep ice core drilling, meteorology and seismic studies were conducted. The camp, with

8176-486: The beginning and end of total solar eclipses. The temperature of the chromosphere increases gradually with altitude, ranging up to around 20,000 K near the top. In the upper part of the chromosphere helium becomes partially ionized . Above the chromosphere, in a thin (about 200 km ) transition region, the temperature rises rapidly from around 20,000 K in the upper chromosphere to coronal temperatures closer to 1,000,000 K . The temperature increase

8288-421: The cheeks and eyelashes glued to the lens of the telescope," after exposure to the freezing cold. The second winter was conducted from February to November 2006 with a team of ten wintering (six French, four Italian and 1 American): The record temperature for this winter was measured at −80 °C on 5 September 2006 at 2:37 ET was renewed several times. The third winter ran from February to November 2007 with

8400-460: The core, but, unlike photons, they rarely interact with matter, so almost all are able to escape the Sun immediately. However, measurements of the number of these neutrinos produced in the Sun are lower than theories predict by a factor of 3. In 2001, the discovery of neutrino oscillation resolved the discrepancy: the Sun emits the number of electron neutrinos predicted by the theory, but neutrino detectors were missing 2 ⁄ 3 of them because

8512-501: The core, converting about 3.7 × 10 protons into alpha particles (helium nuclei) every second (out of a total of ~8.9 × 10 free protons in the Sun), or about 6.2 × 10  kg/s . However, each proton (on average) takes around 9 billion years to fuse with another using the PP chain. Fusing four free protons (hydrogen nuclei) into a single alpha particle (helium nucleus) releases around 0.7% of

8624-401: The corona reaches 1,000,000–2,000,000 K . The high temperature of the corona shows that it is heated by something other than direct heat conduction from the photosphere. It is thought that the energy necessary to heat the corona is provided by turbulent motion in the convection zone below the photosphere, and two main mechanisms have been proposed to explain coronal heating. The first

8736-563: The crew. These experiments are selected over a variety of tests proposed to ESA by European universities and participation from the rest of the crew is voluntary (and highly appreciated). It is important to mention that this research aims not only at improving living conditions for Astronauts in a future human journey to Mars, but the results are also applied directly on society - they help doctors devise therapies for patients with similar difficulties in Europe and elsewhere. Sun The Sun

8848-400: The duration of a solar day on another planet such as Mars . The astronomical symbol for the Sun is a circle with a center dot, [REDACTED] . It is used for such units as M ☉ ( Solar mass ), R ☉ ( Solar radius ) and L ☉ ( Solar luminosity ). The scientific study of the Sun is called heliology . The Sun is a G-type main-sequence star that makes up about 99.86% of

8960-509: The edges of the Antarctic Plateau. Typical wind speed in winter is 2.8 m/s (6 mph). Dome C is situated on top of the Antarctic Polar Plateau, the world's largest frozen desert. No animals or plants live at a distance of more than a few hundred meters from the Southern Ocean . However, south polar skuas have been spotted overflying the station, 1,200 kilometres (750 mi) away from their nearest food sources. It

9072-563: The external poloidal dipolar magnetic field is near its dynamo-cycle minimum strength; but an internal toroidal quadrupolar field, generated through differential rotation within the tachocline, is near its maximum strength. At this point in the dynamo cycle, buoyant upwelling within the convective zone forces emergence of the toroidal magnetic field through the photosphere, giving rise to pairs of sunspots, roughly aligned east–west and having footprints with opposite magnetic polarities. The magnetic polarity of sunspot pairs alternates every solar cycle,

9184-446: The first scientific experience towards a site qualification at Dome C. In 1996, a French-Italian team established a summer camp at Dome C. The two main objectives of the camp were the provision of logistical support for the European Project for Ice Coring in Antarctica (EPICA) and the construction of a permanent research station. The new all-year facility, Concordia Station , became operational in 2005. The first winterover began with

9296-404: The fused mass as energy, so the Sun releases energy at the mass–energy conversion rate of 4.26 billion kg/s (which requires 600 billion kg of hydrogen ), for 384.6  yottawatts ( 3.846 × 10  W ), or 9.192 × 10   megatons of TNT per second. The large power output of the Sun is mainly due to the huge size and density of its core (compared to Earth and objects on Earth), with only

9408-482: The heliosphere, forming the solar magnetic field into a spiral shape, until it impacts the heliopause more than 50 AU from the Sun. In December 2004, the Voyager 1 probe passed through a shock front that is thought to be part of the heliopause. In late 2012, Voyager 1 recorded a marked increase in cosmic ray collisions and a sharp drop in lower energy particles from the solar wind, which suggested that

9520-432: The helium in the Sun would have been produced by Big Bang nucleosynthesis in the first 20 minutes of the universe, and the heavier elements were produced by previous generations of stars before the Sun was formed, and spread into the interstellar medium during the final stages of stellar life and by events such as supernovae . Since the Sun formed, the main fusion process has involved fusing hydrogen into helium. Over

9632-546: The informal name, "Dome C," and that it has precedence over "Dome Circe", a name suggested from Greek mythology after Circe , the bewitching queen of Aeaea island, one of the children of solar god Helios and the Oceanid nymph Perse , who changed men into animals by magic, by members of the SPRI airborne radio echo sounding team in 1982. Later, it was named "Dome Concordia" after that same French/Italian scientific base. Dome C

9744-505: The mass of the Solar System. It has an absolute magnitude of +4.83, estimated to be brighter than about 85% of the stars in the Milky Way , most of which are red dwarfs . It is more massive than 95% of the stars within 7 pc (23 ly). The Sun is a Population I , or heavy-element-rich, star. Its formation approximately 4.6 billion years ago may have been triggered by shockwaves from one or more nearby supernovae . This

9856-444: The neutrinos had changed flavor by the time they were detected. The Sun has a stellar magnetic field that varies across its surface. Its polar field is 1–2 gauss (0.0001–0.0002  T ), whereas the field is typically 3,000 gauss (0.3 T) in features on the Sun called sunspots and 10–100 gauss (0.001–0.01 T) in solar prominences . The magnetic field varies in time and location. The quasi-periodic 11-year solar cycle

9968-419: The optical turbulence is concentrated within the first 30 m atmospheric level at Dome C. The rest of the atmosphere is very quiet with a seeing of about 0.3-0.4 arcseconds , and the overall seeing is somewhat around 1.0 arcseconds. Launched in 2007, PAIX the first robotic multi-color Antarctica Photometer gives a new insight to cope with unresolved stellar enigma and stellar oscillation challenges and offers

10080-478: The outside world using an Iridium phone. Since Concordia Station is a prime space mission analogue, the European Space Agency conducts biomedical research there in collaboration with the French ( IPEV ) and Italian ( ENEA / PNRA ) Antarctic programs. Living conditions upon Dome C simulate what Astronauts have to go through in long-duration spaceflights. To name a few of the common challenges that

10192-419: The past 4.6 billion years, the amount of helium and its location within the Sun has gradually changed. The proportion of helium within the core has increased from about 24% to about 60% due to fusion, and some of the helium and heavy elements have settled from the photosphere toward the center of the Sun because of gravity . The proportions of heavier elements are unchanged. Heat is transferred outward from

10304-414: The photospheric surface. Both coronal mass ejections and high-speed streams of solar wind carry plasma and the interplanetary magnetic field outward into the Solar System. The effects of solar activity on Earth include auroras at moderate to high latitudes and the disruption of radio communications and electric power . Solar activity is thought to have played a large role in the formation and evolution of

10416-455: The planets is weak and does not significantly affect the shape of the Sun. The Sun rotates faster at its equator than at its poles . This differential rotation is caused by convective motion due to heat transport and the Coriolis force due to the Sun's rotation. In a frame of reference defined by the stars, the rotational period is approximately 25.6 days at the equator and 33.5 days at

10528-473: The poles. Viewed from Earth as it orbits the Sun, the apparent rotational period of the Sun at its equator is about 28 days. Viewed from a vantage point above its north pole, the Sun rotates counterclockwise around its axis of spin. A survey of solar analogs suggest the early Sun was rotating up to ten times faster than it does today. This would have made the surface much more active, with greater X-ray and UV emission. Sun spots would have covered 5–30% of

10640-557: The poloidal to the toroidal field, but with a polarity that is opposite to the previous cycle. The process carries on continuously, and in an idealized, simplified scenario, each 11-year sunspot cycle corresponds to a change, then, in the overall polarity of the Sun's large-scale magnetic field. The Sun's magnetic field leads to many effects that are collectively called solar activity . Solar flares and coronal mass ejections tend to occur at sunspot groups. Slowly changing high-speed streams of solar wind are emitted from coronal holes at

10752-448: The primordial Solar System. Typically, the solar heavy-element abundances described above are measured both by using spectroscopy of the Sun's photosphere and by measuring abundances in meteorites that have never been heated to melting temperatures. These meteorites are thought to retain the composition of the protostellar Sun and are thus not affected by the settling of heavy elements. The two methods generally agree well. The core of

10864-470: The probe had passed through the heliopause and entered the interstellar medium , and indeed did so on August 25, 2012, at approximately 122 astronomical units (18 Tm) from the Sun. The heliosphere has a heliotail which stretches out behind it due to the Sun's peculiar motion through the galaxy. On April 28, 2021, NASA's Parker Solar Probe encountered the specific magnetic and particle conditions at 18.8 solar radii that indicated that it penetrated

10976-437: The shorter wavelengths. Solar ultraviolet radiation ionizes Earth's dayside upper atmosphere, creating the electrically conducting ionosphere . Ultraviolet light from the Sun has antiseptic properties and can be used to sanitize tools and water. This radiation causes sunburn , and has other biological effects such as the production of vitamin D and sun tanning . It is the main cause of skin cancer . Ultraviolet light

11088-425: The solar cycle progresses toward its maximum , sunspots tend to form closer to the solar equator, a phenomenon known as Spörer's law . The largest sunspots can be tens of thousands of kilometers across. An 11-year sunspot cycle is half of a 22-year Babcock –Leighton dynamo cycle, which corresponds to an oscillatory exchange of energy between toroidal and poloidal solar magnetic fields. At solar-cycle maximum,

11200-408: The study of chronic hypobaric hypoxia, stress secondary to confinement and isolation, circadian rhythm and sleep disruption, individual and group psychology, telemedicine, and astrobiology. Concordia station has been proposed as one of the real-life Earth-based analogues for long-duration deep-space missions. In the 1970s, Dome C was the site of ice core drilling by field teams of several nations. In

11312-417: The surface. The rotation rate was gradually slowed by magnetic braking , as the Sun's magnetic field interacted with the outflowing solar wind. A vestige of this rapid primordial rotation still survives at the Sun's core, which has been found to be rotating at a rate of once per week; four times the mean surface rotation rate. The Sun consists mainly of the elements hydrogen and helium . At this time in

11424-431: The tachocline picks up heat and expands, thereby reducing its density and allowing it to rise. As a result, an orderly motion of the mass develops into thermal cells that carry most of the heat outward to the Sun's photosphere above. Once the material diffusively and radiatively cools just beneath the photospheric surface, its density increases, and it sinks to the base of the convection zone, where it again picks up heat from

11536-424: The temperature of the corona, at least some of its heat is known to be from magnetic reconnection . The corona is the extended atmosphere of the Sun, which has a volume much larger than the volume enclosed by the Sun's photosphere. A flow of plasma outward from the Sun into interplanetary space is the solar wind . The heliosphere, the tenuous outermost atmosphere of the Sun, is filled with solar wind plasma and

11648-422: The tenuous layers above the photosphere. The photosphere has a particle density of ~10  m (about 0.37% of the particle number per volume of Earth's atmosphere at sea level). The photosphere is not fully ionized—the extent of ionization is about 3%, leaving almost all of the hydrogen in atomic form. The Sun's atmosphere is composed of five layers: the photosphere, the chromosphere , the transition region ,

11760-404: The top of the radiative zone and the convective cycle continues. At the photosphere, the temperature has dropped 350-fold to 5,700 K (9,800 °F) and the density to only 0.2 g/m (about 1/10,000 the density of air at sea level, and 1 millionth that of the inner layer of the convective zone). The thermal columns of the convection zone form an imprint on the surface of the Sun giving it

11872-424: The total mass of the Solar System. Roughly three-quarters of the Sun's mass consists of hydrogen (~73%); the rest is mostly helium (~25%), with much smaller quantities of heavier elements, including oxygen , carbon , neon , and iron . The Sun is a G-type main-sequence star (G2V), informally called a yellow dwarf , though its light is actually white. It formed approximately 4.6 billion years ago from

11984-418: The transfer of energy through this zone is by radiation instead of thermal convection. Ions of hydrogen and helium emit photons, which travel only a brief distance before being reabsorbed by other ions. The density drops a hundredfold (from 20 000 kg/m to 200 kg/m ) between 0.25 solar radii and 0.7 radii, the top of the radiative zone. The radiative zone and the convective zone are separated by

12096-503: The utmost care. Those going outside travelled at least in pairs and were equipped with a radio, spare batteries and a full fleece suit, with only the eyes at times visible. Italian Glaciologist Emanuele Salvietti had to take snow samples every day one kilometre from the base. As he had to walk (because no vehicle operates at these temperatures), he built a full face mask, with only a pipe to breathe. The slightest mistake would lead to certain injury, as astronomer Agabi Karim explained: "Burns on

12208-560: Was below 36 meters. A telescope built on a tower could rise above this " boundary layer " and achieve excellent seeing. The boundary layer is 200 metres (660 ft) at the South Pole and may be as low as 20 metres (66 ft) at Dome A . An earlier paper considered the site and concluded that "Dome C is the best ground-based site to develop a new astronomical observatory". This shows a measured superior seeing of 0.27 arcseconds, half as large as at Mauna Kea Observatory . This figure

12320-421: Was only made in 2005. During this period, the station is inaccessible, requiring total autonomy. The first winter began in mid-February 2005, with thirteen wintering (eleven French people and two Italians): In September 2005 the highest temperature was −48 °C, with an average in August of −60.2 °C and a record of −78.6 °C on 1 September. At these temperatures, trips outside had to be performed with

12432-1541: Was selected as NASA Astronomy Picture of the Day (APOD) on 23 September 2015 . The eleventh wintering is taking place from February 2015 to November 2015 with a team of 13 people (six French, five Italian, one British and one Swiss): The twelfth winter began on February 10, 2016, with twelve overwintering (five Italian, six French, one Belgian): The thirteenth winter began on February 9, 2017, with thirteen overwintering (five French, seven Italian, one Belgian Canadian): The fourteenth winter began on February 6, 2018, with thirteen overwintering (five French, seven Italian, one Austrian): The fifteenth winter began on February 13, 2019, with thirteen overwintering (five French, six Italian, one Danish and one Australian): The sixteenth winter began on February 7, 2020, with twelve overwintering (seven French, four Italian, one Dutch): The seventeenth winter began on January 31, 2021, with twelve overwintering (five French, six Italian, one British): The eighteenth winter began on 7 February 2022, with thirteen overwintering (six French, six Italian and one Swedish): The nineteenth winter began on 7 February 2023, with twelve overwintering (six French, five Italian and one German): The twentieth winter began on 31st January 2024, with thirteen overwintering (seven French, five Italian and one Swiss): The twenty-first winter will begin in February 2025, with thirteen overwintering (six French, six Italian and one British): Dome C In

12544-443: Was taken with an instrument insensitive to near-ground turbulence and so it is comparable to the 0.35 arcseconds Agabi et al. measured for "free atmospheric seeing". The 2004 experiments to measure the astronomical conditions at the site were unattended, controlled by a computer system that had to supervise the generation of its own electricity using a jet-fuel powered Stirling engine . The computer, running Linux , communicated with

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