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58-518: Beta Eridani is the star's Bayer designation . It has the traditional name Cursa derived from Al Kursiyy al Jauzah , "the Chair (or "Footstool") of the Central One". This is the name of the star association consisting of this star along with Lambda Eridani , Psi Eridani and Tau Orionis . According to a NASA catalogue of stars, Al Kursiyy al Jauzah was the title of three stars: β Eri

116-424: A corona and hence is not a source of hard X-ray emission . However, small scale magnetic fields may still be present in the lower atmosphere, resulting from convection turbulence near the surface. The measured strength of the magnetic field on Aldebaran is 0.22  G . Any resulting soft X-ray emissions from this region may be attenuated by the chromosphere , although ultraviolet emission has been detected in

174-469: A 643-day orbit at a separation of 2.0 AU (300 Gm) in a mildly eccentric orbit. However, all three stars surveyed showed similar oscillations yielding similar companion masses, and the authors concluded that the variation was likely to be intrinsic to the star rather than due to the gravitational effect of a companion. In 2015 a study showed stable long-term evidence for both a planetary companion and stellar activity. An asteroseismic analysis of

232-569: A close distance to Aldebaran and similar proper motions. With a parallax of 47.25  milliarcseconds , this translates into a distance of 21.16  pc (69.0  ly ). The NASA Exoplanet Archive recognizes Aldebaran as a binary star, with Aldebaran B being the secondary star. A spectral type of M2.5 has been published for Alpha Tauri B. Alpha Tauri CD is a binary system with the C and D component stars gravitationally bound to and co-orbiting each other. These co-orbiting stars have been shown to be located far beyond Aldebaran and are members of

290-463: A constellation by class: all the first-magnitude stars (in some order), followed by all the second-magnitude stars, and so on. Within each magnitude class, Bayer made no attempt to arrange stars by relative brightness. As a result, the brightest star in each class did not always get listed first in Bayer's order—and the brightest star overall did not necessarily get the designation "Alpha". A good example

348-400: A constellation in rough order of apparent brightness , from brightest to dimmest. The order is not necessarily a precise labeling from brightest to dimmest: in Bayer's day stellar brightness could not be measured precisely. Instead, stars were traditionally assigned to one of six magnitude classes (the brightest to first magnitude, the dimmest to sixth), and Bayer typically ordered stars within

406-491: A different constellation. Bayer's Gamma and Omicron Scorpii, for example, were later reassigned from Scorpius to Libra and given the new names Sigma and Upsilon Librae . (To add to the confusion, the star now known as Omicron Scorpii was not named by Bayer but was assigned the designation o Scorpii (Latin lowercase 'o') by Lacaille—which later astronomers misinterpreted as omicron once Bayer's omicron had been reassigned to Libra.) A few stars no longer lie (according to

464-577: A distance of approximately 65 light-years from the Sun. The star lies along the line of sight to the nearby Hyades cluster . Aldebaran is a red giant , meaning that it is cooler than the Sun with a surface temperature of 3,900  K , but its radius is about 45 times the Sun's , so it is over 400 times as luminous . As a giant star , it has moved off the main sequence on the Hertzsprung–Russell diagram after depleting its supply of hydrogen in

522-592: A few stars too far south to be seen from Germany, but later astronomers (including Nicolas-Louis de Lacaille and Benjamin Apthorp Gould ) supplemented Bayer's catalog with entries for southern constellations. Bayer assigned a lowercase Greek letter (alpha (α), beta (β), gamma (γ), etc.) or a Latin letter (A, b, c, etc.) to each star he catalogued, combined with the Latin name of the star's parent constellation in genitive (possessive) form. The constellation name

580-563: A giant star, but around 25 times lower than the Earth's and 700 times lower than the Sun's. Its metallicity is about 30% lower than the Sun 's. Measurements by the Hipparcos satellite and other sources put Aldebaran around 65.3 light-years (20.0 parsecs) away. Asteroseismology has determined that it is about 16% more massive than the Sun, yet it shines with 518 times the Sun's luminosity due to

638-408: A smaller amplitude, with some showing almost no variation. Hipparcos photometry shows an amplitude of only about 0.02 magnitudes and a possible period around 18 days. Intensive ground-based photometry showed variations of up to 0.03 magnitudes and a possible period around 91 days. Analysis of observations over a much longer period still find a total amplitude likely to be less than 0.1 magnitudes, and

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696-617: A star's radial velocity from the amount of Doppler shift in the spectrum. By this means, the recession velocity of Aldebaran was estimated as 30 miles per second (48 km/s), using measurements performed at Potsdam Observatory by Hermann C. Vogel and his assistant Julius Scheiner . Aldebaran was observed using an interferometer attached to the Hooker Telescope at the Mount Wilson Observatory in 1921 in order to measure its angular diameter , but it

754-787: Is Cursa , Psi Eridani Al Kursiyy al Jauzah I , and Lambda Eridani Al Kursiyy al Jauzah II (excluding Tau Orionis ). 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 a table of the first two batches of names approved by the WGSN; which included Cursa for this star. In Chinese , 玉井 ( Yù Jǐng ), "the Jade Well ", refers to an asterism consisting of β Eridani, λ Eridani , ψ Eridani and τ Orionis . Consequently,

812-489: Is a giant star that has evolved off the main sequence band of the HR diagram after exhausting the hydrogen at its core. The collapse of the center of the star into a degenerate helium core has ignited a shell of hydrogen outside the core and Aldebaran is now on the red giant branch (RGB). The effective temperature of Aldebaran's photosphere is 3,910  K . It has a surface gravity of 1.59  cgs , typical for

870-461: Is a star located in the zodiac constellation of Taurus . It has the Bayer designation α Tauri , which is Latinized to Alpha Tauri and abbreviated Alpha Tau or α Tau. Aldebaran varies in brightness from an apparent visual magnitude 0.75 down to 0.95, making it the brightest star in the constellation, as well as (typically) the fourteenth-brightest star in the night sky. It is positioned at

928-458: Is a stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name. The original list of Bayer designations contained 1,564 stars. The brighter stars were assigned their first systematic names by the German astronomer Johann Bayer in 1603, in his star atlas Uranometria . Bayer catalogued only

986-527: Is a member of the Ursa Major supergroup , an association of stars that share a common origin and motion through space. However, its photometric properties indicate that it may instead be an interloper. Beta Eridani has an optical companion star with an apparent magnitude 10.90 at an angular separation of 120  arcseconds and a position angle of 148°. It has the catalogue identifier CCDM J05079-0506B. Bayer designation A Bayer designation

1044-578: Is a popular subject for ancient and modern myths. As the brightest star in a Zodiac constellation, it is given great significance within astrology . Irish singer and composer, Enya, has written a piece called “Aldebaran” after the star. The name Aldebaran or Alpha Tauri has been adopted many times, including The star also appears in works of fiction such as Far from the Madding Crowd (1874) and Down and Out in Paris and London (1933). It

1102-574: Is frequently abbreviated to a standard three-letter form. For example, Aldebaran in the constellation Taurus (the Bull) is designated α Tauri (abbreviated α Tau , pronounced Alpha Tauri ), which means "Alpha of the Bull". Bayer used Greek letters for the brighter stars, but the Greek alphabet has only twenty-four letters, while a single constellation may contain fifty or more stars visible to

1160-630: Is frequently seen in science fiction , including the Lensman series (1948–1954), Fallen Dragon (2001) and passingly in Kim Stanley Robinson's "Blue Mars" (1996). Aldebaran is associated with Hastur , also known as The King in Yellow, in the horror stories of Robert W. Chambers . Aldebaran regularly features in conspiracy theories as one of the origins of extraterrestrial aliens , often linked to Nazi UFOs . A well-known example

1218-557: Is the German conspiracy theorist Axel Stoll , who considered the star the home of the Aryan race and the target of expeditions by the Wehrmacht . The planetary exploration probe Pioneer 10 is no longer powered or in contact with Earth, but its trajectory is taking it in the general direction of Aldebaran. It is expected to make its closest approach in about two million years. The Austrian chemist Carl Auer von Welsbach proposed

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1276-400: Is the constellation Gemini , where Pollux is Beta Geminorum and the slightly dimmer Castor is Alpha Geminorum. In addition, Bayer did not always follow the magnitude class rule; he sometimes assigned letters to stars according to their location within a constellation, or the order of their rising, or to historical or mythological details. Occasionally the order looks quite arbitrary. Of

1334-782: The Aitken Double Star Catalogue as ADS 3321. It was included with an 11th-magnitude companion as a double star as H IV 66 in the Herschel Catalogue of Double Stars and Σ II 2 in the Struve Double Star Catalog , and together with a 14th-magnitude star as β 550 in the Burnham Double Star Catalogue . Aldebaran is one of the easiest stars to find in the night sky , partly due to its brightness and partly due to being near one of

1392-463: The Chinese name for β Eridani itself is "the third star of Jade Well" ( 玉井三 Yù Jǐng sān ). In older texts, Yu Jing was also spelt Yuh Tsing . β Eridani has a spectral type of A3 III, with the luminosity class III indicating that this is a giant star which has consumed the hydrogen at its core and evolved away from the main sequence . The effective temperature of

1450-559: The Hipparcos catalogue number 21421, mostly seen in scientific publications. It is a variable star listed in the General Catalogue of Variable Stars , but it is listed using its Bayer designation and does not have a separate variable star designation . Aldebaran and several nearby stars are included in double star catalogues such as the Washington Double Star Catalog as WDS 04359+1631 and

1508-646: The core . The star spins slowly and takes 520 days to complete a rotation. Aldebaran is believed to host a planet several times the mass of Jupiter , named Aldebaran b . The traditional name Aldebaran derives from the Arabic al Dabarān ( الدبران ), meaning ' the follower ' , because it seems to follow the Pleiades . In 2016, the International Astronomical Union Working Group on Star Names (WGSN) approved

1566-472: The spectrum . The star is currently losing mass at a rate of (1–1.6) × 10   M ☉ /yr (about one Earth mass in 300,000 years) with a velocity of 30 km/s . This stellar wind may be generated by the weak magnetic fields in the lower atmosphere. Beyond the chromosphere of Aldebaran is an extended molecular outer atmosphere ( MOLsphere ) where the temperature is cool enough for molecules of gas to form. This region lies at about 2.5 times

1624-742: The 88 modern constellations, there are at least 30 in which Alpha is not the brightest star, and four of those lack a star labeled "Alpha" altogether. The constellations with no Alpha-designated star include Vela and Puppis —both formerly part of Argo Navis , whose Greek-letter stars were split among three constellations. Canopus , the former α Argus, is now α Carinae in the modern constellation Carina . Norma's Alpha and Beta were reassigned to Scorpius and re-designated N and H Scorpii respectively, leaving Norma with no Alpha. Francis Baily died before designating an Alpha in Leo Minor , so it also has no Alpha. (The star 46 Leonis Minoris would have been

1682-628: The Greek letters, Bayer sometimes used the leftover Greek letters for miscellaneous labels as well. Ptolemy designated four stars as "border stars", each shared by two constellations: Alpheratz (in Andromeda and Pegasus ), Elnath (in Taurus and Auriga ), Nu Boötis ( Nu and Nu )(in Boötes and Hercules ) and Fomalhaut (in Piscis Austrinus and Aquarius ). Bayer assigned

1740-493: The Hyades star cluster. As with the rest of the stars in the cluster they do not physically interact with Aldebaran in any way. In 1993 radial velocity measurements of Aldebaran, Arcturus and Pollux showed that Aldebaran exhibited a long-period radial velocity oscillation, which could be interpreted as a substellar companion . The measurements for Aldebaran implied a companion with a minimum mass 11.4 times that of Jupiter in

1798-566: The Tropic of Cancer. In Cygnus , for example, Bayer's fixed stars run through g , and on this chart Bayer employs H through P as miscellaneous labels, mostly for neighboring constellations. Bayer did not intend such labels as catalog designations, but some have survived to refer to astronomical objects: P Cygni for example is still used as a designation for Nova Cyg 1600. Tycho's Star ( SN 1572 ), another "temporary star", appears as B Cassiopeiae. In charts for constellations that did not exhaust

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1856-497: The chain of stars π , π , π , π , π and π Orionis . The most stars given the same Bayer designation but with an extra number attached to it is Psi Aurigae . ( ψ , ψ , ψ , ψ , ψ , ψ , ψ , ψ , ψ , ψ , although according to the modern IAU constellation boundaries, ψ lies in Lynx ). Aldebaran Aldebaran ( Arabic : الدَّبَران , lit.   'The Follower') (Proto-Semitic *dVbr- “bee”)

1914-505: The cluster that forms the bull's-head-shaped asterism is more than twice as far away, at about 150 light years. Aldebaran is 5.47 degrees south of the ecliptic and so can be occulted by the Moon . Such occultations occur when the Moon's ascending node is near the autumnal equinox . A series of 49 occultations occurred starting on 29 January 2015 and ending at 3 September 2018. Each event

1972-545: The expanded radius. The angular diameter of Aldebaran has been measured many times. The value adopted as part of the Gaia benchmark calibration is 20.580 ± 0.030  mas . It is 44 times the diameter of the Sun , approximately 61 million kilometres. Aldebaran is a slightly variable star , assigned to the slow irregular type LB . The General Catalogue of Variable Stars indicates variation between apparent magnitude 0.75 and 0.95 from historical reports. Modern studies show

2030-452: The first three of these stars a Greek letter from both constellations: Alpha Andromedae = Delta Pegasi , Beta Tauri = Gamma Aurigae , and Nu Boötis = Psi Herculis . (He catalogued Fomalhaut only once, as Alpha Piscis Austrini .) When the International Astronomical Union (IAU) assigned definite boundaries to the constellations in 1930, it declared that stars and other celestial objects can belong to only one constellation. Consequently,

2088-546: The lines of nine elements, including iron , sodium , calcium , and magnesium . In 1886, Edward C. Pickering at the Harvard College Observatory used a photographic plate to capture fifty absorption lines in the spectrum of Aldebaran. This became part of the Draper Catalogue , published in 1890. By 1887, the photographic technique had improved to the point that it was possible to measure

2146-484: The modern constellation boundaries) within the constellation for which they are named. The proper motion of Rho Aquilae , for example, carried it across the boundary into Delphinus in 1992. A further complication is the use of numeric superscripts to distinguish neighboring stars that Bayer (or a later astronomer) labeled with a common letter. Usually these are double stars (mostly optical doubles rather than true binary stars ), but there are some exceptions such as

2204-462: The more noticeable asterisms in the sky. Following the three stars of Orion's belt in the direction opposite to Sirius , the first bright star encountered is Aldebaran. It is best seen at midnight between late November and early December. The star is, by chance, in the line of sight between the Earth and the Hyades , so it has the appearance of being the brightest member of the open cluster , but

2262-689: The naked eye. When the Greek letters ran out, Bayer continued with Latin letters: uppercase A , followed by lowercase b through z (omitting j and v , but o was included), for a total of another 24 letters. Bayer did not label "permanent" stars with uppercase letters (except for A , which he used instead of a to avoid confusion with α ). However, a number of stars in southern constellations have uppercase letter designations, like B Centauri and G Scorpii . These letters were assigned by later astronomers, notably Lacaille in his Coelum Australe Stelliferum and Gould in his Uranometria Argentina . Lacaille followed Bayer's use of Greek letters, but this

2320-444: The north. This, as well as observations of the changing positions of stars Sirius and Arcturus , led to the discovery of proper motion . Based on present day observations, the position of Aldebaran has shifted 7′ in the last 2000 years; roughly a quarter the diameter of the full moon . Due to precession of the equinoxes , 5,000 years ago the vernal equinox was close to Aldebaran. Between 420,000 and 210,000 years ago, Aldebaran

2378-400: The number of stars, so he also used uppercase Latin letters such as N Velorum and Q Puppis . Lacaille assigned uppercase letters between R and Z in several constellations, but these have either been dropped to allow the assignment of those letters to variable stars or have actually turned out to be variable. In most constellations, Bayer assigned Greek and Latin letters to stars within

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2436-405: The obvious candidate.) In Orion , Bayer first designated Betelgeuse and Rigel , the two 1st-magnitude stars (those of magnitude 1.5 or less), as Alpha and Beta from north to south, with Betelgeuse (the shoulder) coming ahead of Rigel (the foot), even though the latter is usually the brighter. (Betelgeuse is a variable star and can at its maximum occasionally outshine Rigel.) Bayer then repeated

2494-409: The outer envelope is about 8,104 K, which gives the star a white hue typical of A-type stars. The projected rotational velocity is a rapid 196 km s , compared to 2 km s along the Sun 's equator . The star is known to vary in apparent visual magnitude , ranging between 2.72 and 2.80. A particularly strong flare-up was reported in 1985. The location and trajectory of this star suggest that it

2552-459: The procedure for the stars of the 2nd magnitude, labeling them from gamma through zeta in "top-down" (north-to-south) order. Letters as far as Latin p were used for stars of the sixth magnitude. Although Bayer did not use uppercase Latin letters (except A ) for "fixed stars", he did use them to label other items shown on his charts, such as neighboring constellations, "temporary stars", miscellaneous astronomical objects, or reference lines like

2610-587: The proper name Aldebaran for this star. Aldebaran is the brightest star in the constellation Taurus and so has the Bayer designation α Tauri, Latinised as Alpha Tauri. It has the Flamsteed designation 87 Tauri as the 87th star in the constellation of approximately 7th magnitude or brighter, ordered by right ascension . It also has the Bright Star Catalogue number 1457, the HD number 29139, and

2668-612: The radius of the star and has a temperature of about 1,500  K . The spectrum reveals lines of carbon monoxide , water , and titanium oxide . Outside the MOLSphere, the stellar wind continues to expand until it reaches the termination shock boundary with the hot, ionized interstellar medium that dominates the Local Bubble , forming a roughly spherical astrosphere with a radius of around 1000 au , centered on Aldebaran. Five faint stars appear close to Aldebaran in

2726-466: The redundant second designation in each pair above has dropped out of use. Bayer assigned two stars duplicate names by mistake: Xi Arietis (duplicated as Psi Ceti ) and Kappa Ceti ( Kappa and Kappa ) (duplicated as g Tauri ). He corrected these in a later atlas, and the duplicate names were no longer used. Other cases of multiple Bayer designations arose when stars named by Bayer in one constellation were transferred by later astronomers to

2784-448: The residuals to the planet fit has determined that Aldebaran b has a minimum mass of 5.8 ± 0.7 Jupiter masses , and that when the star was on the main sequence it would have given this planet Earth-like levels of illumination and therefore, potentially, temperature. This would place it and any of its moons in the habitable zone . Follow-up study in 2019 have found the evidence for planetary existence inconclusive though. Aldebaran

2842-470: The same proper motion and parallax as Aldebaran and thus may be a physical binary system. These measurements are difficult, since the dim B component appears so close to the bright primary star, and the margin of error is too large to establish (or exclude) a physical relationship between the two. So far neither the B component, nor anything else, has been unambiguously shown to be physically associated with Aldebaran. The Gaia Data Release 3 again suggest

2900-399: The sky. These double star components were given upper-case Latin letter designations more or less in the order of their discovery, with the letter A reserved for the primary star. Some characteristics of these components, including their position relative to Aldebaran, are shown in the table. Some surveys, for example Gaia Data Release 2 , have indicated that Alpha Tauri B may have about

2958-535: The sun around May 30 of each year. With a near- infrared J band magnitude of −2.1, only Betelgeuse (−2.9), R Doradus (−2.6), and Arcturus (−2.2) are brighter at that wavelength. On 11 March AD 509, a lunar occultation of Aldebaran was observed in Athens , Greece . English astronomer Edmund Halley studied the timing of this event, and in 1718 concluded that Aldebaran must have changed position since that time, moving several minutes of arc further to

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3016-411: The variation is considered to be irregular. The photosphere shows abundances of carbon , oxygen , and nitrogen that suggest the giant has gone through its first dredge-up stage—a normal step in the evolution of a star into a red giant during which material from deep within the star is brought up to the surface by convection . With its slow rotation, Aldebaran lacks a dynamo needed to generate

3074-474: Was diverging from Aldebaran, and hence they were not physically connected. However, the companion discovered by Burnham had almost exactly the same proper motion as Aldebaran, suggesting that the two formed a wide binary star system. Working at his private observatory in Tulse Hill , England , in 1864 William Huggins performed the first studies of the spectrum of Aldebaran, where he was able to identify

3132-422: Was insufficient for many constellations. He used first the lowercase letters, starting with a , and if needed the uppercase letters, starting with A , thus deviating somewhat from Bayer's practice. Lacaille used the Latin alphabet three times over in the large constellation Argo Navis , once for each of the three areas that are now the constellations of Carina , Puppis and Vela . That was still insufficient for

3190-549: Was not resolved in these observations. The extensive history of observations of Aldebaran led to it being included in the list of 33 stars chosen as benchmarks for the Gaia mission to calibrate derived stellar parameters. It had previously been used to calibrate instruments on board the Hubble Space Telescope . Aldebaran is listed as the spectral standard for type K5+ III stars . Its spectrum shows that it

3248-596: Was originally نَيِّر اَلدَّبَرَان ( Nayyir al-Dabarān in Arabic), meaning ' the bright one of the follower ' , since it follows the Pleiades; in fact, the Arabs sometimes also applied‍ the name al-Dabarān to the Hyades as a whole. A variety of transliterated spellings have been used, with the current Aldebaran becoming standard relatively recently. This easily seen and striking star in its suggestive asterism

3306-521: Was the brightest star in the night sky, peaking in brightness 320,000 years ago with an apparent magnitude of −1.54 . English astronomer William Herschel discovered a faint companion to Aldebaran in 1782; an 11th-magnitude star at an angular separation of 117 ″ . This star was shown to be itself a close double star by S. W. Burnham in 1888, and he discovered an additional 14th-magnitude companion at an angular separation of 31″. Follow-on measurements of proper motion showed that Herschel's companion

3364-399: Was visible from points in the northern hemisphere or close to the equator ; people in e.g. Australia or South Africa can never observe an Aldebaran occultation since it is too far south of the ecliptic. A reasonably accurate estimate for the diameter of Aldebaran was obtained during the occultation of 22 September 1978. In the 2020s, Aldebaran is in conjunction in ecliptic longitude with

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