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63-539: Tair may refer to: Tair is derived from " altair ", the Arabic word for a bird. TAIR may refer to : Tairov may refer to : Altair Altair is the brightest star in the constellation of Aquila and the twelfth-brightest star in the night sky . It has the Bayer designation Alpha Aquilae, which is Latinised from α Aquilae and abbreviated Alpha Aql or α Aql . Altair

126-425: A number of sine waves , with periods that range between 0.8 and 1.5 hours. It is a weak source of coronal X-ray emission, with the most active sources of emission being located near the star's equator. This activity may be due to convection cells forming at the cooler equator. The angular diameter of Altair was measured interferometrically by R. Hanbury Brown and his co-workers at Narrabri Observatory in

189-410: A sudden increase of the radiative flux emitted from small regions of the corona. They are very complex phenomena, visible at different wavelengths; they involve several zones of the solar atmosphere and many physical effects, thermal and not thermal, and sometimes wide reconnections of the magnetic field lines with material expulsion. Flares are impulsive phenomena, of average duration of 15 minutes, and

252-650: A table of the first two batches of names approved by the WGSN, which included Altair for this star. It is now so entered in the IAU Catalog of Star Names. Along with β Aquilae and γ Aquilae , Altair forms the well-known line of stars sometimes referred to as the Family of Aquila or Shaft of Aquila . Altair is a type-A main-sequence star with about 1.8 times the mass of the Sun and 11 times its luminosity . It

315-565: A velocity at the equator of approximately 286 km/s. This is a significant fraction of the star's estimated breakup speed of 400 km/s. A study with the Palomar Testbed Interferometer revealed that Altair is not spherical, but is flattened at the poles due to its high rate of rotation. Other interferometric studies with multiple telescopes, operating in the infrared , have imaged and confirmed this phenomenon. α Aquilae ( Latinised to Alpha Aquilae )

378-409: Is a balance in loop energy sources and sinks, coronal loops can last for long periods of time and are known as steady state or quiescent coronal loops ( example ). Coronal loops are very important to our understanding of the current coronal heating problem . Coronal loops are highly radiating sources of plasma and are therefore easy to observe by instruments such as TRACE . An explanation of

441-526: Is about 5 000 – 8 000 K , and so they are usually considered as chromospheric features. In 2013, images from the High Resolution Coronal Imager revealed never-before-seen "magnetic braids" of plasma within the outer layers of these active regions. Coronal loops are the basic structures of the magnetic solar corona. These loops are the closed-magnetic flux cousins of the open-magnetic flux that can be found in coronal holes and

504-588: Is an A-type main-sequence star with an apparent visual magnitude of 0.77 and is one of the vertices of the Summer Triangle asterism ; the other two vertices are marked by Deneb and Vega . It is located at a distance of 16.7 light-years (5.1 parsecs ) from the Sun . Altair is currently in the G-cloud —a nearby interstellar cloud , an accumulation of gas and dust. Altair rotates rapidly, with

567-482: Is emphasized by the analysis of the dynamics of the main structures of the corona, which evolve at differential times. Studying coronal variability in its complexity is not easy because the times of evolution of the different structures can vary considerably: from seconds to several months. The typical sizes of the regions where coronal events take place vary in the same way, as it is shown in the following table. Flares take place in active regions and are characterized by

630-426: Is far less dense than the photosphere, and produces about one-millionth as much visible light. The corona is separated from the photosphere by the relatively shallow chromosphere . The exact mechanism by which the corona is heated is still the subject of some debate, but likely possibilities include episodic energy releases from the pervasive magnetic field and magnetohydrodynamic waves from below. The outer edges of

693-668: Is known as Hé Gǔ ( 河鼓 ; lit. "river drum"). The Chinese name for Altair is thus Hé Gǔ èr ( 河鼓二 ; lit. "river drum two", meaning the "second star of the drum at the river"). However, Altair is better known by its other names: Qiān Niú Xīng ( 牵牛星 / 牽牛星 ) or Niú Láng Xīng ( 牛郎星 ), translated as the cowherd star . These names are an allusion to a love story, The Cowherd and the Weaver Girl , in which Niulang (represented by Altair) and his two children (represented by β Aquilae and γ Aquilae ) are separated from respectively their wife and mother Zhinu (represented by Vega) by

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756-419: Is more twisted. Associated with sunspots are coronal loops , loops of magnetic flux , upwelling from the solar interior. The magnetic flux pushes the hotter photosphere aside, exposing the cooler plasma below, thus creating the relatively dark sun spots. High-resolution X-ray images of the Sun's corona photographed by Skylab in 1973, by Yohkoh in 1991–2001, and by subsequent space-based instruments revealed

819-463: Is not properly a gas, because it is made of charged particles, basically protons and electrons, moving at different velocities. Supposing that they have the same kinetic energy on average (for the equipartition theorem ), electrons have a mass roughly 1 800 times smaller than protons, therefore they acquire more velocity. Metal ions are always slower. This fact has relevant physical consequences either on radiative processes (that are very different from

882-494: Is one of the asterisms used by Bugis sailors for navigation, called bintoéng timoro , meaning "eastern star". A group of Japanese scientists sent a radio signal to Altair in 1983 with the hopes of contacting extraterrestrial life. NASA announced Altair as the name of the Lunar Surface Access Module (LSAM) on December 13, 2007. The Russian-made Beriev Be-200 Altair seaplane is also named after

945-506: Is the particle number density , k B {\displaystyle k_{B}} the Boltzmann constant and T {\displaystyle T} the plasma temperature. It is evident from the equation that the plasma pressure lowers when the plasma temperature decreases with respect to the surrounding regions or when the zone of intense magnetic field empties. The same physical effect renders sunspots apparently dark in

1008-544: Is the star's Bayer designation . The traditional name Altair has been used since medieval times. It is an abbreviation of the Arabic phrase النسر الطائر Al-Nisr Al-Ṭa'ir , " the flying eagle ". In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016 included

1071-490: Is thought to be a young star close to the zero age main sequence at about 100 million years old, although previous estimates gave an age closer to one billion years old. Altair rotates rapidly, with a rotational period of under eight hours; for comparison, the equator of the Sun makes a complete rotation in a little more than 25 days, but Altair's rotation is similar to, and slightly faster than, those of Jupiter and Saturn . Like those two planets, its rapid rotation causes

1134-616: Is typically obscured by diffuse sky radiation and glare from the solar disk, but can be easily seen by the naked eye during a total solar eclipse or with a specialized coronagraph . Spectroscopic measurements indicate strong ionization in the corona and a plasma temperature in excess of 1 000 000 kelvins , much hotter than the surface of the Sun, known as the photosphere . Corona ( Latin for 'crown') is, in turn, derived from Ancient Greek κορώνη ( korṓnē )  'garland, wreath'. In 1724, French-Italian astronomer Giacomo F. Maraldi recognized that

1197-567: Is very complex. However, two kinds of basic structures can be distinguished: As for temporal dynamics, three different phases are generally distinguished, whose duration are not comparable. The durations of those periods depend on the range of wavelengths used to observe the event: Sometimes also a phase preceding the flare can be observed, usually called as "pre-flare" phase. Often accompanying large solar flares and prominences are coronal mass ejections (CME). These are enormous emissions of coronal material and magnetic field that travel outward from

1260-561: The Milky Way . They are only permitted to meet once a year, when magpies form a bridge to allow them to cross the Milky Way. The people of Micronesia called Altair Mai-lapa , meaning "big/old breadfruit", while the Māori people called this star Poutu-te-rangi , meaning "pillar of heaven". In Western astrology , the star was ill-omened, portending danger from reptiles . This star

1323-508: The wedge-tailed eagle , and β and γ Aquilae are his two wives the black swans . The people of the Murray River knew the star as Totyerguil . The Murray River was formed when Totyerguil the hunter speared Otjout , a giant Murray cod , who, when wounded, churned a channel across southern Australia before entering the sky as the constellation Delphinus . In Chinese belief, the asterism consisting of Altair, β Aquilae and γ Aquilae

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1386-612: The 11-year solar cycle and becomes particularly simple during the minimum period, when the magnetic field of the Sun is almost similar to a dipolar configuration (plus a quadrupolar component). The interconnections of active regions are arcs connecting zones of opposite magnetic field, of different active regions. Significant variations of these structures are often seen after a flare. Some other features of this kind are helmet streamers – large, cap-like coronal structures with long, pointed peaks that usually overlie sunspots and active regions. Coronal streamers are considered to be sources of

1449-589: The 1960s. They found a diameter of 3   milliarcseconds . Although Hanbury Brown et al. realized that Altair would be rotationally flattened, they had insufficient data to experimentally observe its oblateness. Later, using infrared interferometric measurements made by the Palomar Testbed Interferometer in 1999 and 2000, Altair was found to be flattened. This work was published by G. T. van Belle , David R. Ciardi and their co-authors in 2001. Theory predicts that, owing to Altair's rapid rotation, its surface gravity and effective temperature should be lower at

1512-545: The NASA Parker Solar Probe will approach the Sun very closely, allowing more direct observations. Large-scale structures are very long arcs which can cover over a quarter of the solar disk but contain plasma less dense than in the coronal loops of the active regions. They were first detected in the June 8, 1968, flare observation during a rocket flight. The large-scale structure of the corona changes over

1575-664: The Palomar and Navy interferometers, together with new measurements made by the VINCI instrument at the VLTI . Altair is one of the few stars for which a direct image has been obtained. In 2006 and 2007, J. D. Monnier and his coworkers produced an image of Altair's surface from 2006 infrared observations made with the MIRC instrument on the CHARA array interferometer; this was the first time

1638-563: The Sun at up to 3000 km/s, containing roughly 10 times the energy of the solar flare or prominence that accompanies them. Some larger CMEs can propel hundreds of millions of tons of material into interplanetary space at roughly 1.5 million kilometers an hour. Coronal stars are ubiquitous among the stars in the cool half of the Hertzsprung–Russell diagram . These coronae can be detected using X-ray telescopes . Some stellar coronae, particularly in young stars, are much more luminous than

1701-452: The Sun's chromosphere, which was called helium (from Greek helios 'sun'). French astronomer Jules Jenssen noted, after comparing his readings between the 1871 and 1878 eclipses, that the size and shape of the corona changes with the sunspot cycle . In 1930, Bernard Lyot invented the "coronograph" (now "coronagraph") , which allows viewing the corona without a total eclipse. In 1952, American astronomer Eugene Parker proposed that

1764-418: The Sun's corona are constantly being transported away, creating the "open" magnetic flux entrained in the solar wind . The corona is not always evenly distributed across the surface of the Sun. During periods of quiet, the corona is more or less confined to the equatorial regions, with coronal holes covering the polar regions. However, during the Sun's active periods, the corona is evenly distributed over

1827-664: The Sun's. For example, FK Comae Berenices is the prototype for the FK Com class of variable star . These are giants of spectral types G and K with an unusually rapid rotation and signs of extreme activity. Their X-ray coronae are among the most luminous ( L x ≥ 10 erg·s or 10 W) and the hottest known with dominant temperatures up to 40 MK. The astronomical observations planned with the Einstein Observatory by Giuseppe Vaiana and his group showed that F-, G-, K- and M-stars have chromospheres and often coronae much like

1890-484: The Sun. The O-B stars , which do not have surface convection zones, have a strong X-ray emission. However these stars do not have coronae, but the outer stellar envelopes emit this radiation during shocks due to thermal instabilities in rapidly moving gas blobs. Also A-stars do not have convection zones but they do not emit at the UV and X-ray wavelengths. Thus they appear to have neither chromospheres nor coronae. The matter in

1953-540: The X-ray emission. Coronal holes are unipolar regions which look dark in the X-rays since they do not emit much radiation. These are wide zones of the Sun where the magnetic field is unipolar and opens towards the interplanetary space. The high speed solar wind arises mainly from these regions. In the UV images of the coronal holes, some small structures, similar to elongated bubbles, are often seen as they were suspended in

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2016-510: The aura visible during a solar eclipse belongs to the Sun, not to the Moon . In 1809, Spanish astronomer José Joaquín de Ferrer coined the term 'corona'. Based on his own observations of the 1806 solar eclipse at Kinderhook (New York), de Ferrer also proposed that the corona was part of the Sun and not of the Moon. English astronomer Norman Lockyer identified the first element unknown on Earth in

2079-412: The chromosphere and transition region; and flares and coronal mass ejections (CME) happen in the corona and chromosphere. If flares are very violent, they can also perturb the photosphere and generate a Moreton wave . On the contrary, quiescent prominences are large, cool, dense structures which are observed as dark, "snake-like" Hα ribbons (appearing like filaments) on the solar disc. Their temperature

2142-456: The corona, estimates had put it somewhere between 10 and 20 solar radii from the surface of the Sun. On April 28, 2021, during its eighth flyby of the Sun, NASA's Parker Solar Probe encountered the specific magnetic and particle conditions at 18.8 solar radii that indicated that it penetrated the Alfvén surface. A portrait, as diversified as the one already pointed out for the coronal features,

2205-425: The corona. Often, the solar plasma will fill these loops from one point and drain to another, called foot points ( siphon flow due to a pressure difference, or asymmetric flow due to some other driver). When the plasma rises from the foot points towards the loop top, as always occurs during the initial phase of a compact flare, it is defined as chromospheric evaporation. When the plasma rapidly cools and falls toward

2268-401: The coronal heating problem remains as these structures are being observed remotely, where many ambiguities are present (i.e., radiation contributions along the line-of-sight propagation ). In-situ measurements are required before a definitive answer can be determined, but due to the high plasma temperatures in the corona, in-situ measurements are, at present, impossible. The next mission of

2331-407: The equator and their extension increases during the periods of maximum of the solar cycle, while they almost disappear during each minimum. Therefore, the quiet Sun always coincides with the equatorial zone and its surface is less active during the maximum of the solar cycle. Approaching the minimum of the solar cycle (also named butterfly cycle), the extension of the quiet Sun increases until it covers

2394-498: The equator, making the equator less luminous than the poles. This phenomenon, known as gravity darkening or the von Zeipel effect , was confirmed for Altair by measurements made by the Navy Precision Optical Interferometer in 2001, and analyzed by Ohishi et al. (2004) and Peterson et al. (2006). Also, A. Domiciano de Souza et al. (2005) verified gravity darkening using the measurements made by

2457-413: The equatorial and polar regions, though it is most prominent in areas with sunspot activity. The solar cycle spans approximately 11 years, from one solar minimum to the following minimum. Since the solar magnetic field is continually wound up due to the faster rotation of mass at the Sun's equator ( differential rotation ), sunspot activity is more pronounced at solar maximum where the magnetic field

2520-453: The external part of the solar atmosphere is in the state of plasma , at very high temperature (a few million kelvin) and at very low density (of the order of 10 particles/m ). According to the definition of plasma, it is a quasi-neutral ensemble of particles which exhibits a collective behaviour. The composition is similar to that in the Sun's interior, mainly hydrogen, but with much greater ionization of its heavier elements than that found in

2583-478: The high temperature of the coronal plasma, revealing that the corona is much hotter than the internal layers of the chromosphere. The corona behaves like a gas which is very hot but very light at the same time: the pressure in the corona is usually only 0.1 to 0.6 Pa in active regions, while on the Earth the atmospheric pressure is about 100 kPa, approximately a million times higher than on the solar surface. However it

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2646-482: The most energetic events can last several hours. Flares produce a high and rapid increase of the density and temperature. An emission in white light is only seldom observed: usually, flares are only seen at extreme UV wavelengths and into the X-rays, typical of the chromospheric and coronal emission. In the corona, the morphology of flares is described by observations in the UV, soft and hard X-rays, and in Hα wavelengths, and

2709-455: The photosphere, it is called chromospheric condensation. There may also be symmetric flow from both loop foot points, causing a build-up of mass in the loop structure. The plasma may cool rapidly in this region (for a thermal instability), its dark filaments obvious against the solar disk or prominences off the Sun's limb . Coronal loops may have lifetimes in the order of seconds (in the case of flare events), minutes, hours or days. Where there

2772-459: The photosphere. Bright points are small active regions found on the solar disk. X-ray bright points were first detected on April 8, 1969, during a rocket flight. The fraction of the solar surface covered by bright points varies with the solar cycle. They are associated with small bipolar regions of the magnetic field. Their average temperature ranges from 1.1 MK to 3.4 MK. The variations in temperature are often correlated with changes in

2835-487: The photosphere. Heavier metals, such as iron, are partially ionized and have lost most of the external electrons. The ionization state of a chemical element depends strictly on the temperature and is regulated by the Saha equation in the lowest atmosphere, but by collisional equilibrium in the optically thin corona. Historically, the presence of the spectral lines emitted from highly ionized states of iron allowed determination of

2898-408: The photospheric radiative processes), or on thermal conduction. Furthermore, the presence of electric charges induces the generation of electric currents and high magnetic fields. Magnetohydrodynamic waves (MHD waves) can also propagate in this plasma, even though it is still not clear how they can be transmitted or generated in the corona. Coronal plasma is optically thin and therefore transparent to

2961-468: The same volume: the "F-corona" (for "Fraunhofer"), the "K-corona" (for "Kontinuierlich"), and the "E-corona" (for "emission"). The "F-corona" is named for the Fraunhofer spectrum of absorption lines in ordinary sunlight, which are preserved by reflection off small material objects. The F-corona is faint near the Sun itself, but drops in brightness only gradually far from the Sun, extending far across

3024-444: The sky and becoming the zodiacal light . The F-corona is recognized to arise from small dust grains orbiting the Sun; these form a tenuous cloud that extends through much of the solar system. The "K-corona" is named for the fact that its spectrum is a continuum, with no major spectral features. It is sunlight light that is Thomson-scattered by free electrons in the hot plasma of the Sun's outer atmosphere. The continuum nature of

3087-461: The slow solar wind. Filament cavities are zones which look dark in the X-rays and are above the regions where Hα filaments are observed in the chromosphere. They were first observed in the two 1970 rocket flights which also detected coronal holes . Filament cavities are cooler clouds of plasma suspended above the Sun's surface by magnetic forces. The regions of intense magnetic field look dark in images because they are empty of hot plasma. In fact,

3150-479: The solar corona might be heated by myriad tiny 'nanoflares', miniature brightenings resembling solar flares that would occur all over the surface of the Sun. The high temperature of the Sun's corona gives it unusual spectral features, which led some in the 19th century to suggest that it contained a previously unknown element, " coronium ". Instead, these spectral features have since been explained by highly ionized iron (Fe-XIV, or Fe ). Bengt Edlén , following

3213-421: The solar equator. The average temperature is between two and four million kelvin, while the density goes from 10 to 10 particles per cubic centimetre. Active regions involve all the phenomena directly linked to the magnetic field, which occur at different heights above the Sun's surface: sunspots and faculae occur in the photosphere; spicules , Hα filaments and plages in the chromosphere; prominences in

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3276-403: The solar wind. Loops of magnetic flux well up from the solar body and fill with hot solar plasma. Due to the heightened magnetic activity in these coronal loop regions, coronal loops can often be the precursor to solar flares and CMEs. The solar plasma that feeds these structures is heated from under 6 000 K to well over 10  K from the photosphere, through the transition region, and into

3339-452: The solar wind. These are the coronal plumes. More precisely, they are long thin streamers that project outward from the Sun's north and south poles. The solar regions which are not part of active regions and coronal holes are commonly identified as the quiet Sun. The equatorial region has a faster rotation speed than the polar zones. The result of the Sun's differential rotation is that the active regions always arise in two bands parallel to

3402-567: The spectrum arises from Doppler broadening of the Sun's Fraunhofer absorption lines in the reference frame of the (hot and therefore fast-moving) electrons. Although the K-corona is a phenomenon of the electrons in the plasma, the term is frequently used to describe the plasma itself (as distinct from the dust that gives rise to the F-corona). The "E-corona" is the component of the corona with an emission-line spectrum, either inside or outside

3465-549: The star to be oblate ; its equatorial diameter is over 20 percent greater than its polar diameter. Satellite measurements made in 1999 with the Wide Field Infrared Explorer showed that the brightness of Altair fluctuates slightly, varying by just a few thousandths of a magnitude with several different periods less than 2 hours. As a result, it was identified in 2005 as a Delta Scuti variable star. Its light curve can be approximated by adding together

3528-401: The star. The bright primary star has the multiple star designation WDS  19508+0852A and has several faint visual companion stars, WDS 19508+0852B, C, D, E, F and G. All are much more distant than Altair and not physically associated. Stellar corona The Sun 's corona lies above the chromosphere and extends millions of kilometres into outer space. Coronal light

3591-420: The structure of the corona to be quite varied and complex, leading astronomers to classify various zones on the coronal disc. Astronomers usually distinguish several regions, as described below. Active regions are ensembles of loop structures connecting points of opposite magnetic polarity in the photosphere, the so-called coronal loops. They generally distribute in two zones of activity, which are parallel to

3654-485: The sum of the magnetic pressure and plasma pressure must be constant everywhere on the heliosphere in order to have an equilibrium configuration: where the magnetic field is higher, the plasma must be cooler or less dense. The plasma pressure p {\displaystyle p} can be calculated by the state equation of a perfect gas: p = n k B T {\displaystyle p=nk_{B}T} , where n {\displaystyle n}

3717-516: The surface of any main-sequence star , apart from the Sun, had been imaged. The false-color image was published in 2007. The equatorial radius of the star was estimated to be 2.03 solar radii , and the polar radius 1.63 solar radii—a 25% increase of the stellar radius from pole to equator. The polar axis is inclined by about 60° to the line of sight from the Earth. The term Al Nesr Al Tair appeared in Al Achsasi al Mouakket 's catalogue, which

3780-513: The wavelength band of visible light. It is a phenomenon of the ion component of the plasma, as individual ions are excited by collision with other ions or electrons, or by absorption of ultraviolet light from the Sun. The Sun's corona is much hotter (by a factor from 150 to 450) than the visible surface of the Sun: the corona's temperature is 1 to 3 million kelvin compared to the photosphere 's average temperature – around 5 800 kelvin . The corona

3843-411: The whole disk surface excluding some bright points on the hemisphere and the poles, where there are coronal holes. The Alfvén surface is 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. Researchers were unsure exactly where the Alfvén critical surface of the Sun lay. Based on remote images of

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3906-403: The work of Walter Grotrian in 1939, first identified the coronal spectral lines in 1940 (observed since 1869) as transitions from low-lying metastable levels of the ground configuration of highly ionised metals (the green Fe-XIV line from Fe at 5 303 Å , but also the red Fe-X line from Fe at 6 374 Å ). The solar corona has three recognized, and distinct, sources of light that occupy

3969-490: Was translated into Latin as Vultur Volans . This name was applied by the Arabs to the asterism of Altair, β Aquilae and γ Aquilae and probably goes back to the ancient Babylonians and Sumerians, who called Altair "the eagle star". The spelling Atair has also been used. Medieval astrolabes of England and Western Europe depicted Altair and Vega as birds. The Koori people of Victoria also knew Altair as Bunjil ,

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