Aldebaran (Arabic:الدَّبَران,lit. 'The Follower') is astar in thezodiacconstellation ofTaurus. It has theBayer designationα Tauri, which isLatinized toAlpha Tauri and abbreviated Alpha Tau or α Tau. Aldebaran varies in brightness from anapparent visual magnitude of 0.75 down to 0.95, making it the brightest star in the constellation, as well as (typically) thefourteenth-brightest star in the night sky. It is at a distance of approximately 67light-years. The star lies along the line of sight to the nearbyHyades cluster, but is unrelated and much older than the young cluster.
Aldebaran is ared giant, meaning that it is cooler than the Sun with a surface temperature of3,900 K, but its radius is about 45 timesthe Sun's, so it is over 400 times asluminous. As agiant star, it hasmoved off themain sequence on theHertzsprung–Russell diagram after depleting its supply of hydrogen in thecore. The star spins slowly and takes 520 days to complete a rotation.
Together with the star Alpha Tauri B (Aldebaran B), it makes astar system with an orbital separation of at least 680astronomical units, or 680 times the average distance from Earth to the Sun. The companion has an apparent magnitude of 13.21, hence is 80,000 to 96,000 times fainter than Aldebaran.
Aldebaran is the brightest star in the constellation Taurus, with theBayer designation α Tauri, Latinised as Alpha Tauri. It has theFlamsteed designation 87 Tauri as the 87th star in the constellation of approximately 7th magnitude or brighter, ordered byright ascension. It also has theBright Star Catalogue number 1457, theHD number 29139, and theHipparcos catalogue number 21421, mostly seen in scientific publications.
Aldebaran is one of the easiest stars to find in thenight sky, partly due to its brightness and partly due to being near one of the more noticeableasterisms in the sky. Following the three stars ofOrion's belt in the direction opposite toSirius, the first bright star encountered is Aldebaran.[26]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 theHyades, so it has the appearance of being the brightest member of theopen cluster, but the cluster that forms the bull's-head-shaped asterism is more than twice as far away, at about 150 light years.[27]
Aldebaran is 5.47 degrees south of theecliptic and so can beocculted by theMoon. Such occultations occur when the Moon'sascending node is near theautumnal equinox.[28] A series of 49 occultations occurred starting on 29 January 2015 and ending at 3 September 2018.[29] Each event was visible from points in thenorthern hemisphere or close to theequator. People further south, in Australia orSouth Africa for example, can never observe occultations of Aldebaran because of parallax. The change in position of the Moon relative to the stars due to the effect of parallax means that Aldebaran is too far south of the ecliptic for occultations to be observed. A reasonably accurate estimate for the diameter of Aldebaran was obtained during the occultation of 22 September 1978.[30] In the 2020s, Aldebaran is inconjunction in ecliptic longitude with the sun around May 30 of each year.[31]
Occultation of Aldebaran by theMoon. Aldebaran is the red dot to the right, barely visible in the thumbnail.
On 11 March AD 509, a lunaroccultation of Aldebaran was observed inAthens,Greece.[32] English astronomerEdmund 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 the north. This, as well as observations of the changing positions of starsSirius andArcturus, led to the discovery ofproper motion. Based on present day observations, the position of Aldebaran has shifted 7′ in the last 2000 years; roughly a quarter the diameter of thefull moon.[33][34] Due toprecession of the equinoxes, 5,000 years ago thevernal equinox was close to Aldebaran.[35] Between 420,000 and 210,000 years ago, Aldebaranwas the brightest star in the night sky,[36] peaking in brightness 320,000 years ago with an apparent magnitude of−1.54.[36]
English astronomerWilliam Herschel discovered a faint companion to Aldebaran in 1782;[37] an 11th-magnitude star at anangular separation of 117″. This star was shown to be itself a closedouble star byS. 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 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 widebinary star system.[38]
The extensive history of observations of Aldebaran led to it being included in the list of 33 stars chosen as benchmarks for theGaia mission to calibrate derived stellar parameters.[41] It had previously been used to calibrate instruments on board theHubble Space Telescope.[17]
Theeffective temperature of Aldebaran'sphotosphere is3,900 K. It has a surface gravity of1.45 cgs, typical for a giant star, but around 35 times lower than the Earth's and nearly a thousand times lower than the Sun's. Itsmetallicity is about half theSun's.
Measurements by theHipparcos satellite and other sources put Aldebaran around 65.3 light-years (20.0 parsecs) away.[14] Asteroseismology has determined that it is about 16% more massive than the Sun, yet it shines with 439 times the Sun's luminosity due to the expanded radius. It is 45.1 times thediameter of the Sun, approximately 63 million kilometres. The angular diameter of Aldebaran has been measured many times. The value adopted as part of the Gaia benchmark calibration is20.580±0.030 mas.[17]
Aldebaran is a slightlyvariable star, assigned to theslow irregular typeLB. TheGeneral Catalogue of Variable Stars indicates variation between apparent magnitude 0.75 and 0.95 from historical reports.[4] Modern studies show a smaller amplitude, with some showing almost no variation.[42] Hipparcos photometry shows an amplitude of only about 0.02 magnitudes and a possible period around 18 days.[43] Intensive ground-based photometry showed variations of up to 0.03 magnitudes and a possible period around 91 days.[42] 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.[44]
Thephotosphere shows abundances ofcarbon,oxygen, andnitrogen that suggest the giant has gone through its firstdredge-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 byconvection.[45] With its slow rotation, Aldebaran lacks adynamo needed to generate acorona and hence is not a source ofhard X-ray emission. However, small scalemagnetic 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 is0.22 G.[46] Any resulting soft X-ray emissions from this region may be attenuated by thechromosphere, although ultraviolet emission has been detected in thespectrum.[47] The star is currently losing mass at a rate of(1–1.6)×10−11M☉/yr (about oneEarth mass in 300,000 years) with a velocity of30 km/s.[45] Thisstellar wind may be generated by the weak magnetic fields in the lower atmosphere.[47]
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 about1,500 K. The spectrum reveals lines ofcarbon monoxide,water, andtitanium oxide.[45] Outside the MOLSphere, the stellar wind continues to expand until it reaches thetermination shock boundary with the hot, ionizedinterstellar medium that dominates theLocal Bubble, forming a roughly sphericalastrosphere with a radius of around1000 au, centered on Aldebaran.[48]
Measurements by theGaia spacecraft have identified aproper motion companion to Aldebaran – a star sharing a similar distance and relative motion, which are seen as hints for a physical association between the components.[49] As of 2024[update], it has an angular separation of 33" from Aldebaran along aposition angle of 117°. At its distance, the angular separation implies a physicalprojected separation of 680astronomical units.[50]
The companion star, named Alpha Tauri B[50] or Aldebaran B,[49] has anapparent magnitude of 13.2,[12] which is 80,000 to 96,000 times fainter than Aldebaran.[a] It is also much smaller than Aldebaran, with a radius 0.35 times that of the Sun and a mass 0.400 times that of the Sun.[19] Aspectral type of M2.5 has been published for the star.[12]
Four further stars at least as bright as B appear close to Aldebaran in the sky. Thesedouble star components were given upper-caseLatin 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.
Alpha Tauri CD is abinary 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 the Hyades star cluster. As with the rest of the stars in the cluster they do not physically interact with Aldebaran in any way.[37]
In 1993 radial velocity measurements of Aldebaran,Arcturus andPollux showed that Aldebaran exhibited a long-period radial velocity oscillation, which could be interpreted as asubstellar companion. The measurements for Aldebaran implied a companion with a minimum mass 11.4 times that ofJupiter in a 643-day orbit at a separation of 2.0 AU (300 Gm) in a mildlyeccentric 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.[53]
In 2015 a study led byArtie P. Hatzes showed stable long-term evidence for both a planetary companion and stellar activity.[16] Anasteroseismic analysis of the residuals to the planet fit has determined that Aldebaran b has a minimum mass of5.8±0.7Jupiter 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 have placed it and any of its moons in thehabitable zone.[15] However, a follow-up study in 2019 found that additional data weaken the evidence for a planetary companion.[54] A two-planet solution fits the data better but would be unstable; the more likely explanation is that the radial velocity variations are caused by intrinsic stellar oscillations that mimic a planetary companion, as observed inGamma Draconis[54] and42 Draconis.[55][56] Based on the 2019 study, some subsequent studies of planet candidates around giant stars consider Aldebaran b doubtful or disproven,[57][58] including a 2025 paper with Hatzes as the lead author.[56]
Aldebaran was originallyنَيِّر 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 nameal-Dabarān to the Hyades as a whole.[59] A variety of transliterated spellings have been used, with the currentAldebaran becoming standard relatively recently.[21]
This easily seen and striking star in its suggestiveasterism is a popular subject for ancient and modern myths.
Mexican culture: For theSeris of northwestern Mexico, this star provides light for the seven women giving birth (Pleiades). It has three names:Hant Caalajc Ipápjö,Queeto, andAzoj Yeen oo Caap ('star that goes ahead'). The lunar month corresponding to October is calledQueeto yaao'Aldebaran's path'.[60]
Australian Aboriginal culture: amongst indigenous people of the Clarence River, in north-easternNew South Wales, this star is the ancestorKarambal, 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.[61]
Aside fromal-Dabarān, other traditional Arabic names areʽAin al-Thaur, the eye of Taurus, andal-Fanīq, the large or male camel, with the Hyades beingal-Qilāṣ, the small camels.[59]
TheAncient Greek nameΛαμπαδίαςLampadias, literally'torch-like' or'torch-bearer', was used in Ptolemy'sTetrabiblos.[64]
ALatin name is Palilicium (or Parilicium), so called because this star disappeared in twilight around the time ofParilia, the feast ofPales on April 21.[21] This name appeared inFlamsteed andBode's star catalogues.[59] Another Latin name, used in the medievalAlfonsine Tables, was Cor Tauri, the heart of the bull.[21]
InBiblical Hebrew, עָשׁ (ʿāš) inJob 9:9 and עַ֫יִשׁ (ʿayiš) inJob 38:32 have been identified with it and translated accordingly in English versions such asNJPS andREB.[68]
The planetary exploration probePioneer 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.[74]
^abStock, Stephan; Reffert, Sabine; Quirrenbach, Andreas; Hauschildt, P. (2018). "Precise radial velocities of giant stars. X. Bayesian stellar parameters and evolutionary stages for 372 giant stars from the Lick planet search".Astronomy and Astrophysics.616: A33.arXiv:1805.04094.Bibcode:2018A&A...616A..33S.doi:10.1051/0004-6361/201833111.S2CID119361866.
^abCutri, Roc M.; Skrutskie, Michael F.; Van Dyk, Schuyler D.; Beichman, Charles A.; Carpenter, John M.; Chester, Thomas; Cambresy, Laurent; Evans, Tracey E.; Fowler, John W.; Gizis, John E.; Howard, Elizabeth V.; Huchra, John P.; Jarrett, Thomas H.; Kopan, Eugene L.; Kirkpatrick, J. Davy; Light, Robert M.; Marsh, Kenneth A.; McCallon, Howard L.; Schneider, Stephen E.; Stiening, Rae; Sykes, Matthew J.; Weinberg, Martin D.; Wheaton, William A.; Wheelock, Sherry L.; Zacarias, N. (2003)."VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)".CDS/ADC Collection of Electronic Catalogues.2246: II/246.Bibcode:2003yCat.2246....0C.S2CID115529446.Archived from the original on 2021-04-21. Retrieved2021-11-16.
^abDucati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system".CDS/ADC Collection of Electronic Catalogues.2237: 0.Bibcode:2002yCat.2237....0D.
^Burnham, S.W. (1900). "A General Catalogue of the Double Stars discovered by S. W. Burnham from 1871 to 1899, arranged in order of Right Ascension".Publications of the Yerkes Observatory.1:59–60.Bibcode:1900PYerO...1....1B.
^Können, G. P.; Meeus, J. (1972). "Occultation series of five stars".Journal of the British Astronomical Association.82: 431.Bibcode:1972JBAA...82..431K.
^Freedman, Immanuel (2015). "The Marduk Star Nēbiru".Cuneiform Digital Library Bulletin: 3.
^abTomkin, Jocelyn (April 1998). "Once and Future Celestial Kings".Sky and Telescope.95 (4):59–63.Bibcode:1998S&T....95d..59T. – based on computations fromHIPPARCOS data. (The calculations exclude stars whose distance orproper motion is uncertain.)PDF[dead link]
^Gore, John Ellard (1904)."Stellar Satellites".Studies in astronomy. Chatto & Windus. pp. 107–109.Archived from the original on 2023-07-22. Retrieved2015-07-21.
^abWasatonic, Rick; Guinan, Edward F. (1997). "Aldebaran: Discovery of Small Amplitude Light Variations".Information Bulletin on Variable Stars.4480: 1.Bibcode:1997IBVS.4480....1W.
^Percy, J. R.; Terziev, E. (2011). "Studies of "Irregularity" in Pulsating Red Giants. III. Many More Stars, an Overview, and Some Conclusions".Journal of the American Association of Variable Star Observers (Jaavso).39 (1): 1.Bibcode:2011JAVSO..39....1P.
^abGonzález-Payo, J.; Caballero, J. A.; Gorgas, J.; Cortés-Contreras, M.; Gálvez-Ortiz, M.-C.; Cifuentes, C. (2024-07-29). "Multiplicity of stars with planets in the solar neighbourhood".Astronomy and Astrophysics.689: A302.arXiv:2407.20138.Bibcode:2024A&A...689A.302G.doi:10.1051/0004-6361/202450048.
^Seow, C. L. (2013).Job 1-21: interpretation and commentary. Illuminations. Grand Rapids, Michigan Cambridge, U.K: William B. Eerdmans Publishing Company. p. 559.ISBN978-0-8028-4895-6.
^Partridge, Jamie (2015-04-30)."Fixed Star Aldebaran".Astrology King.Archived from the original on 2022-05-21. Retrieved2022-06-27.
^de Lafayette, Maximilien (2012).Genetic Aliens. From Aldebaran to the Pentagon, Area 51 and Aliens Genetic Laboratories at Dulce Base. Lulu.com.ISBN978-1300879527.[self-published source]
^Van Helsing, Jan (1997).Unternehmen Aldebaran. Kontakte mit Menschen aus einem anderen Sonnensystem [Operation Aldebaran. Contacts with humans from another star system] (in German). Lathen: Ewertlag.ISBN3-89478-220-X.
^Stoll, Axel (2004).Hochtechnologie im Dritten Reich [High Tech in the Third Reich] (in German). Rottenburg:Kopp Verlag. p. 111ff.ISBN978-3930219858.
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