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For other uses, see Aldebaran (disambiguation). Not to be confused with Alderamin, Alderaan, or Alderaan (astronomy).
Taurus constellation map.svg
The position of Aldebaran in the Taurus constellation.
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Taurus
Pronunciation /ælˈdɛbərən/[1][2]
Right ascension 04h 35m 55.23907s[3]
Declination +16° 30′ 33.4885″[3]
Apparent magnitude (V) 0.86[4] (0.75-0.95)[5]
Evolutionary stage Giant star
Spectral type K5 III[6]
Apparent magnitude (J) −2.095[7]
U−B color index +1.92[4]
B−V color index +1.44[4]
Variable type LB[5]
Radial velocity (Rv) +54.26±0.03[8] km/s
Proper motion (μ) RA: 63.45±0.84[3] mas/yr
Dec.: −189.94±0.65[3] mas/yr
Parallax (π) 49.97 ± 0.75[9] mas
Distance 65.3 ± 1.0 ly
(20.0 ± 0.3 pc)
Absolute magnitude (MV) −0.641±0.034[9]
Mass 1.5±0.3[10] M
Radius 44.2±0.9[11] R
Luminosity 518±32[12] L
Surface gravity (log g) 1.59[12] cgs
Temperature 3,910[12] K
Metallicity [Fe/H] –0.34[12] dex
Rotation 643 days[13]
Other designations
87 Tauri, Alpha Tauri, BD+16°629, GJ 171.1, GJ 9159, HD 29139, HIP 21421, HR 1457, SAO 94027
Database references

Aldebaran, designated Alpha Tauri (α Tauri, abbreviated Alpha Tau, α Tau), is an orange giant star located about 65 light years from the Sun in the zodiac constellation of Taurus. It is the brightest star in its constellation and usually the fourteenth-brightest star in the nighttime sky, though it varies slowly in brightness between magnitude 0.75 and 0.95. It is likely that Aldebaran hosts a planet several times the size of Jupiter.

The planetary exploration probe Pioneer 10 is currently heading in the general direction of the star and should make its closest approach in about two million years.[14]


Alpha Tauri is the star's Bayer designation. The name Aldebaran is Arabic (الدبران al-dabarān) and means "the Follower", presumably because it rises near and soon after the Pleiades.[15] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[16] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[17] included a table of the first two batches of names approved by the WGSN; which included Aldebaran for this star. It is now so entered in the IAU Catalog of Star Names.[18]

Names in other languages[edit]

In Persia it was known as Tascheter.

The Romans called it Palilicium.

In the Middle Ages it was sometimes called Cor Tauri (the Heart of the Bull/Taurus).

John Gower refers to it as Aldeboran.[19]

In Chinese it is known as 畢宿五 (Bìxiùwŭ, the Fifth Star of the Net).

In Hindu astronomy it is identified as the lunar mansion Rohini ("the red one") and as one of the twenty-seven daughters of Daksha and the wife of the god Chandra (moon).


This easily seen and striking star in its suggestive asterism is a popular subject for ancient and modern myths.

  • Mexican culture: For the Seris of northwestern Mexico, this star provides light for the seven women giving birth (Pleiades). It has three names: Hant Caalajc Ipápjö, Queeto, and Azoj Yeen oo Caap ("star that goes ahead"). The lunar month corresponding to October is called Queeto yaao "Aldebaran's path".[20]
  • Aboriginal culture: in the Clarence River of northeastern New South Wales, 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.[21]

Observation history[edit]

On March 11, of 509 AD, a lunar occultation of Aldebaran was observed in Athens, Greece.[22] 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 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.[23][24] Note that 5,000 years ago the vernal equinox was close to Aldebaran.[citation needed]

English astronomer William Herschel discovered a faint companion to Aldebaran in 1782;[25] 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 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.[26]

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 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 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.[27]

The angular diameter of this star was measured for the first time in 1921 using an interferometer attached to the Hooker Telescope at the Mount Wilson Observatory. The result was 0.0237″, which was in close agreement with the estimated values of the time.[28]

Physical properties[edit]

Size comparison between Aldebaran and the Sun

Aldebaran is classified as a type K5 III star, which indicates it is an orange-hued giant star that has evolved off the main sequence band of the Hertzsprung–Russell diagram after exhausting the hydrogen at its core. The collapse of the centre of the star into a degenerate helium core has ignited a shell of hydrogen outside the core and Aldebaran is now a red giant.[29] This has caused it to expand to 44.2 times the diameter of the Sun,[11][30] equivalent to approximately 61 million kilometres (see 10 gigametres for similar sizes).

Measurements by the Hipparcos satellite and other sources put Aldebaran around 65.3 light-years (20.0 parsecs) away.[9] Stellar models predict it only has about 50% more mass than the Sun, yet it shines with 425 times the Sun's luminosity due to the expanded radius. Aldebaran is a slightly variable star, of the slow irregular variable type LB. It varies by about 0.2 in apparent magnitude from 0.75 to 0.95.[5] With a near-infrared J band magnitude of −2.1, only Betelgeuse (−2.9), R Doradus (−2.6), and Arcturus (−2.2) are brighter.[7]

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.[10] With its slow rotation, Aldebaran lacks a dynamo needed to generate 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.[31]) Any resulting soft X-ray emissions from this region may be attenuated by the chromosphere, although ultraviolet emission has been detected in the spectrum.[32] The star is currently losing mass at a rate of (1–1.6) × 10−11 M yr−1 with a velocity of 30 km s−1.[10] This stellar wind may be generated by the weak magnetic fields in the lower atmosphere.[32]

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 between 1.2 and 2.8 times the radius of the star, with temperatures of 1,000−2,000 K. The spectrum reveals lines of carbon monoxide, water, and titanium oxide.[10] Past this radius, the modest outflow of the stellar wind itself declines in temperature to about 7,500 K at a distance of 1 Astronomical Unit (AU)−the distance of the Earth from the Sun. The 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 1,000 AU, centered on Aldebaran.[33]


Occultation of Aldebaran by the Moon

Aldebaran is one of the easiest stars to find in the night sky, partly due to its brightness and partly due to its spatial relation to one of the more noticeable asterisms in the sky. If one follows the three stars of Orion's belt from left to right (in the Northern Hemisphere) or right to left (in the Southern), the first bright star found by continuing that line is Aldebaran.

Since the star is located (by chance) in the line of sight between the Earth and the Hyades, it has the appearance of being the brightest member of the more scattered Hyades open star cluster that makes up the bull's-head-shaped asterism; however, the star cluster is actually more than twice as far away, at about 150 light years.

Aldebaran is close enough to the ecliptic to be occulted by the Moon. Such occultations occur when the Moon's ascending node is near the autumnal equinox. A series of 49 occultations occur starting at 29 Jan 2015 and ending at 3 Sep 2018.[34] Each event is visible from a different location on Earth, but always in the northern hemisphere or close to the equator. That means that people in e.g. Australia or South Africa can never observe an Aldebaran occultation. This is due to the fact that Aldebaran is slightly too far south of the ecliptic. A reasonably accurate estimate for the diameter of Aldebaran was obtained during the September 22, 1978 occultation.[35] Aldebaran is in conjunction with the Sun around June 1 of each year.[36]

Occultations by planets are not possible at present, as each planet passes Aldebaran north. The closest conjunction of a planet with Aldebaran in the 21st century occurred on July 9, 2012, when Venus passed Aldebaran 56' northward. However, in the far future and far past occultations of Aldebaran by Mercury and Venus occurred as result of wandering nodes. The next occultation of Aldebaran by a planet, Venus, will occur on 5366 August 27.[citation needed]

Double star[edit]

Five faint stars are positioned so that they appear close to Aldebaran. These double stars were given alphabetic secondary star designations more or less in the order of their discovery, with the letter A reserved for the primary star. Some of the characteristics of these components, including their position relative to Aldebaran, are listed in the table at right.

WDS 04359+1631 Catalogue Entry[37]
α Tau Apparent
B 13.60 31.60″ 113° 2007
C 11.30 129.50″ 32° 2011
D 13.70
E 12.00 36.10″ 323° 2000
F 13.60 255.70″ 121° 2000

Some surveys have indicated that Alpha Tauri B may have about the same proper motion and parallax as Aldebaran and thus may be a physical binary system. However these measurements are difficult to make because the dim B component appears so close to the bright primary star. The resulting margin of error is too large to positively establish (or exclude) a physical relationship between the two stars. So far neither the B component, nor anything else, has been unambiguously shown to be physically associated with Aldebaran.[38]

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 the Hyades star cluster. As with the rest of the stars in the cluster they do not physically interact with Aldebaran in any way.[25]

Claims of a planetary system[edit]

Main article: Aldebaran b

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 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.[39] In 2015 a study showed stable longterm evidence for both a planetary companion and stellar activity.[40]

See also[edit]


  1. ^ Oxford Dictionary: Aldebaran
  2. ^ Merriam-Webster: Aldebaran
  3. ^ a b c d Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653. arXiv:0708.1752Freely accessible. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. 
  4. ^ a b c Ducati, 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. 
  5. ^ a b c "Query= alf Tau". General Catalogue of Variable Stars. Centre de Données astronomiques de Strasbourg. Retrieved 2009-12-16. 
  6. ^ Gray, R. O.; Corbally, C. J.; Garrison, R. F.; McFadden, M. T.; Bubar, E. J.; McGahee, C. E.; O'Donoghue, A. A.; Knox, E. R. (2006). "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc-The Southern Sample". The Astronomical Journal. 132: 161. arXiv:astro-ph/0603770Freely accessible. Bibcode:2006AJ....132..161G. doi:10.1086/504637. 
  7. ^ a b Cutri, R. M.; Skrutskie, M. F.; Van Dyk, S.; Beichman, C. A.; Carpenter, J. M.; Chester, T.; Cambresy, L.; Evans, T.; Fowler, J.; Gizis, J.; Howard, E.; Huchra, J.; Jarrett, T.; Kopan, E. L.; Kirkpatrick, J. D.; Light, R. M.; Marsh, K. A.; McCallon, H.; Schneider, S.; Stiening, R.; Sykes, M.; Weinberg, M.; Wheaton, W. A.; Wheelock, S.; Zacarias, N. (2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". VizieR On-line Data Catalog: II/246. Originally published in: 2003yCat.2246....0C. 2246. Bibcode:2003yCat.2246....0C. 
  8. ^ Famaey, B.; Jorissen, A.; Luri, X.; Mayor, M.; Udry, S.; Dejonghe, H.; Turon, C. (2005). "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters". Astronomy and Astrophysics. 430: 165. arXiv:astro-ph/0409579Freely accessible. Bibcode:2005A&A...430..165F. doi:10.1051/0004-6361:20041272. 
  9. ^ a b c Gatewood, George (July 2008). "Astrometric Studies of Aldebaran, Arcturus, Vega, the Hyades, and Other Regions". The Astronomical Journal. 136 (1): 452–460. Bibcode:2008AJ....136..452G. doi:10.1088/0004-6256/136/1/452. 
  10. ^ a b c d Ohnaka, K. (May 2013). "Spatially resolved, high-spectral resolution observation of the K giant Aldebaran in the CO first overtone lines with VLTI/AMBER". Astronomy & Astrophysics. 553: 8. arXiv:1303.4763Freely accessible. Bibcode:2013A&A...553A...3O. doi:10.1051/0004-6361/201321207. A3. 
  11. ^ a b Richichi, A.; Roccatagliata, V. (2005). "Aldebaran's angular diameter: How well do we know it?". Astronomy & Astrophysics. 433 (1): 305–312. arXiv:astro-ph/0502181Freely accessible. Bibcode:2005A&A...433..305R. doi:10.1051/0004-6361:20041765. We derive an average value of 19.96±0.03 milliarcsec for the uniform disk diameter. The corresponding limb-darkened value is 20.58±0.03 milliarcsec, or 44.2±0.9 R. 
  12. ^ a b c d Piau, L.; et al. (February 2011). "Surface convection and red-giant radius measurements". Astronomy and Astrophysics. 526: A100. arXiv:1010.3649Freely accessible. Bibcode:2011A&A...526A.100P. doi:10.1051/0004-6361/201014442. 
  13. ^ Koncewicz, R.; Jordan, C. (January 2007). "OI line emission in cool stars: calculations using partial redistribution". Monthly Notices of the Royal Astronomical Society. 374 (1): 220–231. Bibcode:2007MNRAS.374..220K. doi:10.1111/j.1365-2966.2006.11130.x. 
  14. ^ Nieto, Michael Martin; Anderson, John D. (January 2007). "Search for a solution of the Pioneer anomaly". Contemporary Physics. 48 (1): 41–54. arXiv:0709.3866Freely accessible. Bibcode:2007ConPh..48...41N. doi:10.1080/00107510701462061. 
  15. ^ Falkner, David E. (2011). "The Winter Constellations". The Mythology of the Night Sky. Patrick Moore's Practical Astronomy Series. p. 19. doi:10.1007/978-1-4614-0137-7_3. ISBN 978-1-4614-0136-0. 
  16. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016. 
  17. ^ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016. 
  18. ^ "IAU Catalog of Star Names". Retrieved 28 July 2016. 
  19. ^ Confessio Amantis VII.1310
  20. ^ Moser, Mary B.; Marlett, Stephen A. (2005). Comcáac quih yaza quih hant ihíip hac: Diccionario seri-español-inglés (PDF) (in Spanish and English). Hermosillo, Sonora and Mexico City: Universidad de Sonora and Plaza y Valdés Editores. 
  21. ^ Clarke, Philip A. (2007). Aboriginal People and Their Plants. New South Wales: Rosenberg Publishing Pty Ltd. p. 30. 
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  27. ^ Clerke, Agnes Mary (1908). A Popular History of Astronomy During the Nineteenth Century (4th ed.). Adam and Charles Black. pp. 381–382, 385, 406. 
  28. ^ Pease, F. G. (June 1921). "The Angular Diameter of a Bootis by the Interferometer". Publications of the Astronomical Society of the Pacific. 33 (193): 171. Bibcode:1921PASP...33..171P. doi:10.1086/123068. 
  29. ^ Inglis, Michael (2015). "Life on the Main Sequence". Astrophysics is Easy!. The Patrick Moore Practical Astronomy Series. p. 155. doi:10.1007/978-3-319-11644-0_10. ISBN 978-3-319-11643-3. 
  30. ^ Richichi & Roccatagliata (2005) derived an angular diameter of 20.58±0.03 milliarcsec, which given a distance of 65 light years yields a diameter of 61 million km.
  31. ^ Aurière, M.; et al. (February 2015). "The magnetic fields at the surface of active single G-K giants". Astronomy & Astrophysics. 574: 30. arXiv:1411.6230Freely accessible. Bibcode:2015A&A...574A..90A. doi:10.1051/0004-6361/201424579. A90. 
  32. ^ a b Ayres, Thomas R.; Brown, Alexander; Harper, Graham M. (November 2003). "Buried Alive in the Coronal Graveyard". The Astrophysical Journal. 598 (1): 610–625. Bibcode:2003ApJ...598..610A. doi:10.1086/378699. 
  33. ^ Wood, Brian E.; et al. (February 2007). "The Wind-ISM Interaction of alpha Tauri". The Astrophysical Journal. 655 (2): 946–957. Bibcode:2007ApJ...655..946W. doi:10.1086/510404. 
  34. ^ Können, G. P.; Meeus, J. (1972). "Occultation series of five stars". Journal of the British Astronomical Association. 82: 431. Bibcode:1972JBAA...82..431K. 
  35. ^ White, N. M. (June 1979). "Lunar occultation of the Hyades and diameters of Alpha Tauri and Theta-1 Tauri". The Astronomical Journal. 84: 872–876. Bibcode:1979AJ.....84..872W. doi:10.1086/112489. 
  36. ^ Star Maps created using XEphem (2008). "LASCO Star Maps (identify objects in the field of view for any day of the year)". Large Angle and Spectrometric Coronagraph Experiment (LASCO). Retrieved 2012-06-01.  2012 (with Venus and Mercury) and 2011
  37. ^ Mason, B. D.; et al. (2014). "The Washington Visual Double Star Catalog". The Astronomical Journal. 122 (6): 3466–3471. Bibcode:2001AJ....122.3466M. doi:10.1086/323920. 
  38. ^ Poveda, A.; et al. (April 1994). "Statistical studies of visual double and multiple stars. II. A catalogue of nearby wide binary and multiple systems". Revista Mexicana de Astronomia y Astrofisica. 28 (1): 43–89. Bibcode:1994RMxAA..28...43P. 
  39. ^ Hatzes, A.; Cochran, W. (1993). "Long-period radial velocity variations in three K giants". The Astrophysical Journal. 413 (1): 339–348. Bibcode:1993ApJ...413..339H. doi:10.1086/173002. 
  40. ^ Hatzes, A. P.; Cochran, W. D.; et al. "Long-lived, long-period radial velocity variations in Aldebaran: A planetary companion and stellar activity". arXiv:1505.03454Freely accessible. Bibcode:2015A&A...580A..31H. doi:10.1051/0004-6361/201425519. 

External links[edit]

Media related to Aldebaran at Wikimedia Commons

Coordinates: Sky map 04h 35m 55.2s, +16° 30′ 33″