Aldebaran
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Aldebaran (Arabic: “The Follower”, "الدبران") is the brightest
star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...
in the
zodiac The zodiac is a belt-shaped region of the sky that extends approximately 8° north or south (as measured in celestial latitude) of the ecliptic, the Sun path, apparent path of the Sun across the celestial sphere over the course of the year. ...
constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...
of
Taurus Taurus is Latin for 'bull' and may refer to: * Taurus (astrology), the astrological sign * Taurus (constellation), one of the constellations of the zodiac * Taurus (mythology), one of two Greek mythological characters named Taurus * '' Bos tauru ...
. 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 Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's lig ...
0.75 down to 0.95, making it (typically) the fourteenth-brightest star in the night sky. It is located at a distance of approximately 65
light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...
s from the Sun. The star lies along the line of sight to the nearby Hyades cluster. Aldebaran is a
giant star A giant star is a star with substantially larger radius and luminosity than a main sequence, main-sequence (or ''dwarf'') star of the same effective temperature, surface temperature.Giant star, entry in ''Astronomy Encyclopedia'', ed. Patrick Moo ...
that is cooler than the Sun with a surface temperature of , but its radius is about 44 times the Sun's, so it is over 400 times as luminous. It spins slowly and takes 520 days to complete a rotation. Aldebaran is believed to host a planet several times the mass of
Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...
, named . The planetary exploration probe
Pioneer 10 ''Pioneer 10'' (originally designated Pioneer F) is an American space probe, launched in 1972 and weighing , that completed the first mission to the planet Jupiter. Thereafter, ''Pioneer 10'' became the first of five artificial objects to ach ...
is heading in the general direction of the star and should make its closest approach in about two million years.


Nomenclature

The traditional name Aldebaran derives from the Arabic ''al Dabarān'' ("الدبران"), meaning "the follower", because it seems to follow the
Pleiades The Pleiades (), also known as The Seven Sisters, Messier 45 and other names by different cultures, is an asterism and an open star cluster containing middle-aged, hot B-type stars in the north-west of the constellation Taurus. At a distance of ...
. In 2016, the
International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...
Working Group on Star Names The International Astronomical Union (IAU) established a Working Group on Star Names (WGSN) in May 2016 to catalog and standardize proper names for stars for the international astronomical community. It operates under Division C – Education ...
(WGSN) approved 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 A Flamsteed designation is a combination of a number and constellation name that uniquely identifies most naked eye stars in the modern constellations visible from southern England. They are named for John Flamsteed who first used them while co ...
87 Tauri as the 87th star in the constellation of approximately 7th magnitude or brighter, ordered by
right ascension Right ascension (abbreviated RA; symbol ) is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the March equinox to the (hour circle of the) point in question above the earth. When paired w ...
. It also has the
Bright Star Catalogue The Bright Star Catalogue, also known as the Yale Catalogue of Bright Stars, Yale Bright Star Catalogue, or just YBS, is a star catalogue that lists all stars of stellar magnitude 6.5 or brighter, which is roughly every star visible to the nak ...
number 1457, the HD number 29139, and the
Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial obj ...
catalogue number 21421, mostly seen in scientific publications. It is a variable star listed in the
General Catalogue of Variable Stars The General Catalogue of Variable Stars (GCVS) is a list of variable stars. Its first edition, containing 10,820 stars, was published in 1948 by the Academy of Sciences of the USSR and edited by B. V. Kukarkin and P. P. Parenago. Second and thi ...
, but it is listed using its Bayer designation and does not have a separate
variable star designation In astronomy, a variable star designation is a unique identifier given to variable stars. It uses a variation on the Bayer designation format, with an identifying label (as described below) preceding the Latin genitive of the name of the constell ...
. Aldebaran and several nearby stars are included in double star catalogues such as the
Washington Double Star Catalog The Washington Double Star Catalog, or WDS, is a catalog of double stars, maintained at the United States Naval Observatory. The catalog contains positions, magnitudes, proper motions and spectral types and has entries for (as of June 2017) 141, ...
as WDS 04359+1631 and the
Aitken Double Star Catalogue The Aitken Double Star Catalogue, or ADS, is a star catalogue of double stars. It was compiled by Robert Grant Aitken and published in 1932 in two volumes, under the name ''New general catalogue of double stars within 120° of the North Pole''. ...
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 The Burnham Double Star Catalogue (BDS) is a catalogue of double stars within 121° of the celestial North Pole. It was published in two parts by the Carnegie Institution of Washington in 1906, under the title ''A General Catalogue of Double Star ...
.


Observation

Aldebaran is one of the easiest stars to find in the
night sky The night sky is the nighttime appearance of celestial objects like stars, planets, and the Moon, which are visible in a clear sky between sunset and sunrise, when the Sun is below the horizon. Natural light sources in a night sky include ...
, partly due to its brightness and partly due to being near one of the more noticeable asterisms in the sky. Following the three stars of
Orion's belt Orion's Belt or the Belt of Orion, also known as the Three Kings or Three Sisters, is an asterism in the constellation Orion. It consists of the three bright stars Alnitak Alnitak is a triple star system in the constellation of ...
in the opposite direction to
Sirius Sirius is the list of brightest stars, brightest star in the night sky. Its name is derived from the Ancient Greek language, Greek word , or , meaning 'glowing' or 'scorching'. The star is designated α Canis Majoris, Latinisation ...
, the first bright star encountered is Aldebaran. It is best seen at midnight late November / early December. The star is, by chance, in the line of sight between the Earth and the
Hyades Hyades may refer to: * Hyades (band) *Hyades (mythology) *Hyades (star cluster) The Hyades (; Greek Ὑάδες, also known as Caldwell 41, Collinder 50, or Melotte 25) is the nearest open cluster and one of the best-studied star clusters. Loca ...
, so it has the appearance of being the brightest member of the
open cluster An open cluster is a type of star cluster made of up to a few thousand stars that were formed from the same giant molecular cloud and have roughly the same age. More than 1,100 open clusters have been discovered within the Milky Way galaxy, and ...
, but 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 The ecliptic or ecliptic plane is the orbital plane of the Earth around the Sun. From the perspective of an observer on Earth, the Sun's movement around the celestial sphere over the course of a year traces out a path along the ecliptic again ...
and so can be occulted by the
Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
. Such occultations occur when the Moon's
ascending node An orbital node is either of the two points where an orbit intersects a plane of reference to which it is inclined. A non-inclined orbit, which is contained in the reference plane, has no nodes. Planes of reference Common planes of reference ...
is near the autumnal equinox. A series of 49 occultations occurred starting on 29 January 2015 and ending at 3 September 2018. Each event was visible from points in the
northern hemisphere The Northern Hemisphere is the half of Earth that is north of the Equator. For other planets in the Solar System, north is defined as being in the same celestial hemisphere relative to the invariable plane of the solar system as Earth's Nort ...
or close to the
equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can als ...
; people in e.g. Australia or
South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...
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 the sun around May 30 of each year. With a near-
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from around ...
J band
magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...
of −2.1, only
Betelgeuse Betelgeuse is a red supergiant of spectral type M1-2 and one of the largest stars visible to the naked eye. It is usually the tenth-brightest star in the night sky and, after Rigel, the second-brightest in the constellation of Orion ...
(−2.9),
R Doradus R Doradus (HD 29712 or P Doradus) is a red giant variable star in the far-southern constellation Dorado. Its distance from Earth is . Having a uniform disk diameter of , it is thought to be the extrasolar star with the largest apparent ...
(−2.6), and
Arcturus , - bgcolor="#FFFAFA" , Note (category: variability): , , H and K emission vary. Arcturus is the brightest star in the northern constellation of Boötes. With an apparent visual magnitude of −0.05, it is the third-brightest of the ...
(−2.2) are brighter at that wavelength.


Observational history

On 11 March AD 509, a lunar
occultation An occultation is an event that occurs when one object is hidden from the observer by another object that passes between them. The term is often used in astronomy, but can also refer to any situation in which an object in the foreground blocks ...
of Aldebaran was observed in
Athens Athens ( ; el, Αθήνα, Athína ; grc, Ἀθῆναι, Athênai (pl.) ) is both the capital and largest city of Greece. With a population close to four million, it is also the seventh largest city in the European Union. Athens dominates ...
,
Greece Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders with ...
. English astronomer
Edmund Halley Edmond (or Edmund) Halley (; – ) was an English astronomer, mathematician and physicist. He was the second Astronomer Royal in Britain, succeeding John Flamsteed in 1720. From an observatory he constructed on Saint Helena in 1676–77, Ha ...
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 the north. This, as well as observations of the changing positions of stars
Sirius Sirius is the list of brightest stars, brightest star in the night sky. Its name is derived from the Ancient Greek language, Greek word , or , meaning 'glowing' or 'scorching'. The star is designated α Canis Majoris, Latinisation ...
and
Arcturus , - bgcolor="#FFFAFA" , Note (category: variability): , , H and K emission vary. Arcturus is the brightest star in the northern constellation of Boötes. With an apparent visual magnitude of −0.05, it is the third-brightest of the ...
, led to the discovery of
proper motion Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...
. 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 The full moon is the lunar phase when the Moon appears fully illuminated from Earth's perspective. This occurs when Earth is located between the Sun and the Moon (when the ecliptic coordinate system, ecliptic longitudes of the Sun and Moon opp ...
. Due to
precession of the equinoxes In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's rotational axis. In the absence of precession, the astronomical body's orbit would show axial parallelism. In particu ...
, 5,000 years ago the vernal equinox was close to Aldebaran. Between 420,000 and 210,000 years ago, Alderbaran was the brightest star in the night sky, – based on computations from
HIPPARCOS ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial obj ...
data. (The calculations exclude stars whose distance or
proper motion Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...
is uncertain.) tp://tlgleonid.asuscomm.com/HITACHI/BOOK_ASTRO/S&T/SkyandTelescope_1998%20-%20astronomy/04/199804059063.pdf PDF/ref> peaking in brightness 320,000 years ago with an apparent magnitude of -1.54. English astronomer
William Herschel Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Caroline H ...
discovered a faint companion to Aldebaran in 1782; an 11th-magnitude star at an
angular separation Angular distance \theta (also known as angular separation, apparent distance, or apparent separation) is the angle between the two sightlines, or between two point objects as viewed from an observer. Angular distance appears in mathematics (in pa ...
of 117 . This star was shown to be itself a close
double star In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes. This occurs because the pair either forms a binary star (i.e. a bi ...
by
S. W. Burnham Sherburne Wesley Burnham (December 12, 1838 – March 11, 1921) was an American astronomer. For more than 50 years Burnham spent all his free time observing the heavens, mainly concerning himself with binary stars. Biography Sherburne ...
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 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 A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in wh ...
system. Working at his private observatory in
Tulse Hill Tulse Hill is a district in the London Borough of Lambeth in South London that sits on Brockwell Park. It is approximately five miles from Charing Cross and is bordered by Brixton, Dulwich, Herne Hill, Streatham and West Norwood. History The ar ...
,
England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...
, in 1864
William Huggins Sir William Huggins (7 February 1824 – 12 May 1910) was an English astronomer best known for his pioneering work in astronomical spectroscopy together with his wife, Margaret. Biography William Huggins was born at Cornhill, Middlesex, in ...
performed the first studies of the spectrum of Aldebaran, where he was able to identify the lines of nine elements, including
iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
,
sodium Sodium is a chemical element with the symbol Na (from Latin ''natrium'') and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable iso ...
,
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to ...
, and
magnesium Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
. In 1886, Edward C. Pickering at the
Harvard College Observatory The Harvard College Observatory (HCO) is an institution managing a complex of buildings and multiple instruments used for astronomical research by the Harvard University Department of Astronomy. It is located in Cambridge, Massachusetts, United St ...
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 a star's
radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...
from the amount of
Doppler shift The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who d ...
in the spectrum. By this means, the recession velocity of Aldebaran was estimated as (48 km/s), using measurements performed at Potsdam Observatory by Hermann C. Vogel and his assistant
Julius Scheiner Julius Scheiner (25 November 1858 – 20 December 1913) was a German astronomer, born in Cologne and educated at Bonn. He became assistant at the astrophysical observatory in Potsdam in 1887 and its observer in chief in 1898, three years after h ...
. Aldebaran was observed using an interferometer attached to the
Hooker Telescope The Mount Wilson Observatory (MWO) is an astronomical observatory in Los Angeles County, California, United States. The MWO is located on Mount Wilson, a peak in the San Gabriel Mountains near Pasadena, northeast of Los Angeles. The observat ...
at the
Mount Wilson Observatory The Mount Wilson Observatory (MWO) is an astronomical observatory in Los Angeles County, California, United States. The MWO is located on Mount Wilson, a peak in the San Gabriel Mountains near Pasadena, northeast of Los Angeles. The observat ...
in 1921 in order to measure its
angular diameter The angular diameter, angular size, apparent diameter, or apparent size is an angular distance describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the visual angle, and in optics, it is ...
, but it 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 ''Gaia'' is a space observatory of the European Space Agency (ESA), launched in 2013 and expected to operate until 2025. The spacecraft is designed for astrometry: measuring the positions, distances and motions of stars with unprecedented preci ...
to calibrate derived stellar parameters. It had previously been used to calibrate instruments on board the
Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...
.


Physical characteristics

Aldebaran is listed as the spectral standard for type K5+ III stars. Its spectrum shows that it is a
giant star A giant star is a star with substantially larger radius and luminosity than a main sequence, main-sequence (or ''dwarf'') star of the same effective temperature, surface temperature.Giant star, entry in ''Astronomy Encyclopedia'', ed. Patrick Moo ...
that has evolved off the
main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...
band of the
Hertzsprung–Russell diagram The Hertzsprung–Russell diagram, abbreviated as H–R diagram, HR diagram or HRD, is a scatter plot of stars showing the relationship between the stars' absolute magnitudes or luminosity, luminosities versus their stellar classifications or eff ...
after exhausting the
hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
at its core. The collapse of the centre of the star into a degenerate
helium Helium (from el, ἥλιος, helios, lit=sun) is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. ...
core has ignited a shell of hydrogen outside the core and Aldebaran is now on the
red giant branch The red-giant branch (RGB), sometimes called the first giant branch, is the portion of the giant branch before helium ignition occurs in the course of stellar evolution. It is a stage that follows the main sequence for low- to intermediate-mass sta ...
(RGB). The
effective temperature The effective temperature of a body such as a star or planet is the temperature of a black body that would emit the same total amount of electromagnetic radiation. Effective temperature is often used as an estimate of a body's surface temperature ...
of Aldebaran's
photosphere The photosphere is a star's outer shell from which light is radiated. The term itself is derived from Ancient Greek roots, φῶς, φωτός/''phos, photos'' meaning "light" and σφαῖρα/''sphaira'' meaning "sphere", in reference to it ...
is . It has a surface gravity of , typical for a giant star, but around 25 times lower than the Earth's and 700 times lower than the Sun's. Its
metallicity In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word ''"metals"'' as a ...
is about 30% lower than the Sun's. Measurements by the
Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial obj ...
satellite and other sources put Aldebaran around away. Asteroseismology has determined that it is about 16% more massive than the
Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
, yet it shines with 518 times the Sun's luminosity due to the expanded radius. The angular diameter of Aldebaran has been measured many times. The value adopted as part of the Gaia benchmark calibration is . It is 44 times the diameter of the Sun, approximately 61 million kilometres. Aldebaran is a slightly
variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as ...
, assigned to the slow irregular type ''LB''. The
General Catalogue of Variable Stars The General Catalogue of Variable Stars (GCVS) is a list of variable stars. Its first edition, containing 10,820 stars, was published in 1948 by the Academy of Sciences of the USSR and edited by B. V. Kukarkin and P. P. Parenago. Second and thi ...
indicates variation between apparent magnitude 0.75 and 0.95 from historical reports. Modern studies show 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 the variation is considered to be irregular. The
photosphere The photosphere is a star's outer shell from which light is radiated. The term itself is derived from Ancient Greek roots, φῶς, φωτός/''phos, photos'' meaning "light" and σφαῖρα/''sphaira'' meaning "sphere", in reference to it ...
shows abundances of
carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent In chemistry, the valence (US spelling) or valency (British spelling) of an element is the measure of its combining capacity with o ...
,
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
, and
nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
that suggest the giant has gone through its first
dredge-up A dredge-up is any one of several stages in the evolution of some stars. By definition, during a ''dredge-up'', a convection zone extends all the way from the star's surface down to the layers of material that have undergone fusion. Consequently, th ...
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 Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...
. With its slow rotation, Aldebaran lacks a
dynamo file:DynamoElectricMachinesEndViewPartlySection USP284110.png, "Dynamo Electric Machine" (end view, partly section, ) A dynamo is an electrical generator that creates direct current using a commutator (electric), commutator. Dynamos were the f ...
needed to generate a
corona Corona (from the Latin for 'crown') most commonly refers to: * Stellar corona, the outer atmosphere of the Sun or another star * Corona (beer), a Mexican beer * Corona, informal term for the coronavirus SARS-CoV-2, which causes the COVID-19 di ...
and hence is not a source of hard X-ray emission. However, small scale
magnetic fields A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
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 
Gauss Johann Carl Friedrich Gauss (; german: Gauß ; la, Carolus Fridericus Gauss; 30 April 177723 February 1855) was a German mathematician and physicist who made significant contributions to many fields in mathematics and science. Sometimes refer ...
. Any resulting soft X-ray emissions from this region may be attenuated by the
chromosphere A chromosphere ("sphere of color") is the second layer of a star's atmosphere, located above the photosphere and below the solar transition region and corona. The term usually refers to the Sun's chromosphere, but not exclusively. In the Su ...
, although ultraviolet emission has been detected in the
spectrum A spectrum (plural ''spectra'' or ''spectrums'') is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors i ...
. The star is currently losing mass at a rate of (about one
Earth mass An Earth mass (denoted as M_\mathrm or M_\oplus, where ⊕ is the standard astronomical symbol for Earth), is a unit of mass equal to the mass of the planet Earth. The current best estimate for the mass of Earth is , with a relative uncertainty ...
in 300,000 years) with a velocity of . 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 the radius of the star and has a temperature of about . The spectrum reveals lines of
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, poisonous, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the simple ...
,
water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
, and
titanium oxide Titanium oxide may refer to: * Titanium dioxide (titanium(IV) oxide), TiO2 * Titanium(II) oxide (titanium monoxide), TiO, a non-stoichiometric oxide * Titanium(III) oxide (dititanium trioxide), Ti2O3 * Ti3O * Ti2O * δ-TiOx (x= 0.68–0.75) * T ...
. Outside the MOLSphere, the stellar wind continues to expand until it reaches the
termination shock The heliosphere is the magnetosphere, astrosphere and outermost atmospheric layer of the Sun. It takes the shape of a vast, bubble-like region of space. In plasma physics terms, it is the cavity formed by the Sun in the surrounding interst ...
boundary with the hot, ionized
interstellar medium In astronomy, the interstellar medium is the matter and radiation that exist in the space between the star systems in a galaxy. This matter includes gas in ionic, atomic, and molecular form, as well as dust and cosmic rays. It fills interstella ...
that dominates the
Local Bubble The Local Bubble, or Local Cavity, is a relative cavity in the interstellar medium (ISM) of the Orion Arm in the Milky Way. It contains the closest of celestial neighbours and among others, the Local Interstellar Cloud (which contains the Sol ...
, forming a roughly spherical astrosphere with a radius of around 1,000 AU, centered on Aldebaran.


Visual companions

Five faint stars appear close to Aldebaran in the sky. These
double star In observational astronomy, a double star or visual double is a pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes. This occurs because the pair either forms a binary star (i.e. a bi ...
components were given upper-case
Latin letter The Latin script, also known as Roman script, is an alphabetic writing system based on the letters of the classical Latin alphabet, derived from a form of the Greek alphabet which was in use in the ancient Greek city of Cumae, in southern Ital ...
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 The ''Gaia'' catalogues are star catalogues created using the results obtained by '' Gaia'' space telescope. The catalogues are released in stages that will contain increasing amounts of information; the early releases also miss some stars, espec ...
, have indicated that Alpha Tauri B may have about the same
proper motion Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...
and
parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...
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. A spectral type of M2.5 has been published for Alpha Tauri B. Alpha Tauri CD is a
binary system A binary system is a system of two astronomical bodies which are close enough that their gravitational attraction causes them to orbit each other around a barycenter ''(also see animated examples)''. More restrictive definitions require that th ...
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 the Hyades star cluster. As with the rest of the stars in the cluster they do not physically interact with Aldebaran in any way.


Planetary system

In 1993 radial velocity measurements of Aldebaran,
Arcturus , - bgcolor="#FFFAFA" , Note (category: variability): , , H and K emission vary. Arcturus is the brightest star in the northern constellation of Boötes. With an apparent visual magnitude of −0.05, it is the third-brightest of the ...
and Pollux showed that Aldebaran exhibited a long-period radial velocity oscillation, which could be interpreted as a
substellar companion A substellar object, sometimes called a substar, is an astronomical object the mass of which is smaller than the smallest mass at which hydrogen fusion can be sustained (approximately 0.08 solar masses). This definition includes brown dwarfs and fo ...
. The measurements for Aldebaran implied a companion with a minimum mass 11.4 times that of
Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...
in a 643-day orbit at a separation of in a mildly
eccentric Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-center, in geometry * Eccentricity (graph theory) of a v ...
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 the residuals to the planet fit has determined that Aldebaran b has a minimum mass of
Jupiter mass Jupiter mass, also called Jovian mass, is the unit of mass equal to the total mass of the planet Jupiter. This value may refer to the mass of the planet alone, or the mass of the entire Jovian system to include the moons of Jupiter. Jupiter is by ...
es, 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 In astronomy and astrobiology, the circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure.J. F. Kas ...
. Follow-up study in 2019 have found the evidence for planetary existence inconclusive though.


Etymology and mythology

Aldebaran 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.


Mythology

This easily seen and striking star in its suggestive asterism is a popular subject for ancient and modern myths. * Mexican culture: For the
Seris The Seri or ''Comcaac'' are an indigenous group of the Mexican state of Sonora. The majority reside on the Seri communal property ( es, ejido), in the towns of Punta Chueca ( sei, Socaaix) and El Desemboque ( sei, Haxöl Iihom, link=no) on th ...
of northwestern Mexico, this star provides light for the seven women giving birth (
Pleiades The Pleiades (), also known as The Seven Sisters, Messier 45 and other names by different cultures, is an asterism and an open star cluster containing middle-aged, hot B-type stars in the north-west of the constellation Taurus. At a distance of ...
). It has three names: ', ', and ' ("star that goes ahead"). The lunar month corresponding to October is called ' "Aldebaran's path". * Aboriginal culture: in the Clarence River of northeastern
New South Wales ) , nickname = , image_map = New South Wales in Australia.svg , map_caption = Location of New South Wales in AustraliaCoordinates: , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , es ...
, this star is the Ancestor ''Karambal'', who stole another man's wife. The woman's husband tracked him down and burned the tree in which he was hiding. It is believed that he rose to the sky as smoke and became the star Aldebaran.


Names in other languages

* In
Hindu astronomy Astronomy has long history in Indian subcontinent stretching from pre-historic to modern times. Some of the earliest roots of Indian astronomy can be dated to the period of Indus Valley civilisation or earlier. Astronomy later developed as a dis ...
it is identified as the lunar mansion Rohini ("the red one") and as one of the twenty-seven daughters of
Daksha In Hinduism, Daksha (Sanskrit: दक्ष, IAST: , lit. "able, dexterous, or honest one") is one of the '' Prajapati'', the agents of creation, as well as a divine king-rishi. His iconography depicts him as a man with a stocky body and a ha ...
and the wife of the god
Chandra Chandra ( sa, चन्द्र, Candra, shining' or 'moon), also known as Soma ( sa, सोम), is the Hindu god of the Moon, and is associated with the night, plants and vegetation. He is one of the Navagraha (nine planets of Hinduism) and ...
(Moon). * In
Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...
it has been called ''Lampadias'', literally "torch-like ''or'' -bearer". * In
Chinese Chinese can refer to: * Something related to China * Chinese people, people of Chinese nationality, citizenship, and/or ethnicity **''Zhonghua minzu'', the supra-ethnic concept of the Chinese nation ** List of ethnic groups in China, people of ...
, (), meaning ''
Net Net or net may refer to: Mathematics and physics * Net (mathematics), a filter-like topological generalization of a sequence * Net, a linear system of divisors of dimension 2 * Net (polyhedron), an arrangement of polygons that can be folded up ...
'', refers to an asterism consisting Aldebaran, ε Tauri, δ3 Tauri, δ1 Tauri, γ Tauri, 71 Tauri and λ Tauri. Consequently, the
Chinese name Chinese names or Chinese personal names are names used by individuals from Greater China and other parts of the Chinese-speaking world throughout East and Southeast Asia (ESEA). In addition, many names used in Japan, Korea and Vietnam are often a ...
for Aldebaran itself is (), "the Fifth Star of Net".


In modern culture

As the brightest star in a Zodiac constellation, it is given great significance within
astrology Astrology is a range of Divination, divinatory practices, recognized as pseudoscientific since the 18th century, that claim to discern information about human affairs and terrestrial events by studying the apparent positions of Celestial o ...
. The name Aldebaran or Alpha Tauri has been adopted many times, including *
Aldebaran Rock Palmer Land () is the portion of the Antarctic Peninsula, Antarctica that lies south of a line joining Cape Jeremy and Cape Agassiz. This application of Palmer Land is consistent with the 1964 agreement between the Advisory Committee on Antarctic N ...
in Antarctica * United States Navy stores ship and Italian frigate ''Aldebaran'' (F 590) * proposed micro-satellite launch vehicle
Aldebaran Aldebaran (Arabic: “The Follower”, "الدبران") is the brightest star 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. Alde ...
* French company
Aldebaran Robotics Nao (pronounced ''now'') is an autonomous, programmable humanoid robot formerly developed by Aldebaran Robotics, a French robotics company headquartered in Paris, which was acquired by SoftBank Group in 2015 and rebranded as SoftBank Robotics. ...
* fashion brand AlphaTauri *
Formula 1 Formula One (also known as Formula 1 or F1) is the highest class of international racing for open-wheel single-seater formula racing cars sanctioned by the Fédération Internationale de l'Automobile (FIA). The World Drivers' Championship, ...
team Scuderia AlphaTauri, previously known as
Toro Rosso Scuderia Toro Rosso (; literal translation of "Red Bull Racing Team"), commonly known as Toro Rosso or by its abbreviation STR, was an Italian Formula One racing team. It was one of two Formula One teams owned by Austrian beverage company Re ...
The star also appears in works of fiction such as ''
Far From the Madding Crowd ''Far from the Madding Crowd'' (1874) is Thomas Hardy's fourth novel and his first major literary success. It originally appeared anonymously as a monthly serial in ''Cornhill Magazine'', where it gained a wide readership. The novel is set in ...
'' (1874) and ''
Down and Out in Paris and London ''Down and Out in Paris and London'' is the first full-length work by the English author George Orwell, published in 1933. It is a memoir in two parts on the theme of poverty in the two cities. Its target audience was the middle- and upper-cl ...
'' (1933). It is frequently seen in
science fiction Science fiction (sometimes shortened to Sci-Fi or SF) is a genre of speculative fiction which typically deals with imaginative and futuristic concepts such as advanced science and technology, space exploration, time travel, parallel unive ...
, including the ''
Lensman series The ''Lensman'' series is a series of science fiction novels by American author E. E. "Doc" Smith. It was a runner-up for the 1966 Hugo award for Best All-Time Series, losing to the ''Foundation'' series by Isaac Asimov. Plot The series begin ...
'' (1948-1954) and '' Fallen Dragon'' (2001). Aldebaran regularly features in
conspiracy theories A conspiracy theory is an explanation for an event or situation that invokes a conspiracy by sinister and powerful groups, often political in motivation, when other explanations are more probable.Additional sources: * * * * The term has a nega ...
as one of the origins of extraterrestrial aliens, often linked to
Nazi UFOs In ufology, conspiracy theory, science fiction, and comic book stories, claims or stories have circulated linking UFOs to Nazi Germany. The German UFO theories describe supposedly successful attempts to develop advanced aircraft or spacecraft pri ...
. A well-known example is the German conspiracy theorist Axel Stoll, who considered the star the home of the
Aryan race The Aryan race is an obsolete historical race concept that emerged in the late-19th century to describe people of Proto-Indo-European heritage as a racial grouping. The terminology derives from the historical usage of Aryan, used by modern I ...
and the target of expeditions by the
Wehrmacht The ''Wehrmacht'' (, ) were the unified armed forces of Nazi Germany from 1935 to 1945. It consisted of the ''Heer'' (army), the ''Kriegsmarine'' (navy) and the ''Luftwaffe'' (air force). The designation "''Wehrmacht''" replaced the previous ...
. The planetary exploration probe
Pioneer 10 ''Pioneer 10'' (originally designated Pioneer F) is an American space probe, launched in 1972 and weighing , that completed the first mission to the planet Jupiter. Thereafter, ''Pioneer 10'' became the first of five artificial objects to ach ...
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 Carl Auer von Welsbach (1 September 1858 – 4 August 1929), who received the Austrian noble title of Freiherr Auer von Welsbach in 1901, was an Austrian scientist and inventor, who separated didymium into the elements neodymium and praseo ...
proposed the name ''aldebaranium'' (chemical symbol Ad) for a
rare earth element The rare-earth elements (REE), also called the rare-earth metals or (in context) rare-earth oxides or sometimes the lanthanides (yttrium and scandium are usually included as rare earths), are a set of 17 nearly-indistinguishable lustrous silv ...
that he (among others) had found. Today, it is called
ytterbium Ytterbium is a chemical element with the symbol Yb and atomic number 70. It is a metal, the fourteenth and penultimate element in the lanthanide series, which is the basis of the relative stability of its +2 oxidation state. However, like the othe ...
(symbol Yb).


See also

*
Lists of stars The following are lists of stars. These are astronomical objects that spend some portion of their existence generating energy through thermonuclear fusion. By location * Lists of stars by constellation By name * List of traditional star names ...
*
List of brightest stars This is a list of stars arranged by their apparent magnitude – their brightness as observed from Earth. It includes all stars brighter than magnitude +2.50 in visible light, measured using a ''V''-band filter in the UBV photometric system. Sta ...
*
List of nearest bright stars This list of nearest bright stars is a table of stars found within 15 parsecs (48.9 light-years) of the nearest star, the Sun, that have an absolute magnitude of +8.5 or brighter, which is approximately comparable to a listing of stars more lumi ...
*
Historical brightest stars The Solar System and all of the visible stars are in different orbits about the core of the Milky Way galaxy. Thus, their relative positions change over time, and for the nearer stars this movement can be measured. As a star moves toward or away ...
*
Taurus (Chinese astronomy) According to traditional Chinese uranography, the modern constellation Taurus is located within the western quadrant of the sky, which is symbolized as the White Tiger of the West (西方白虎) (''Xī Fāng Bái Hǔ''). The name of the western c ...


References


External links

*
Daytime occultation of Aldebaran by the Moon (Moscow, Russia)
YouTube video {{DEFAULTSORT:Aldebaran K-type giants Slow irregular variables Hypothetical planetary systems Taurus (constellation) Tauri, Alpha 1457 Durchmusterung objects Tauri, 087 Gliese and GJ objects 029139 021421
Aldebaran Aldebaran (Arabic: “The Follower”, "الدبران") is the brightest star 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. Alde ...
TIC objects