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Diagram showing star positions and boundaries of the Boötes constellation and its surroundings, according to the International Astronomical Union
Cercle rouge 100%.svg
Arcturus in the constellation of Boötes (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Boötes
Pronunciation /ɑːrkˈtjʊərəs/
Right ascension 14h 15m 39.7s[1]
Declination +19° 10′ 56″[1]
Apparent magnitude (V) −0.05[2]
Spectral type K0 III[3]
Apparent magnitude (J) −2.25[2]
U−B color index +1.28[2]
B−V color index +1.23[2]
R−I color index +0.65[2]
Note (category: variability): H and K emission vary.
Radial velocity (Rv)−5.19[4] km/s
Proper motion (μ) RA: −1093.45[5] mas/yr
Dec.: −1999.40[5] mas/yr
Parallax (π)88.83 ± 0.54[1] mas
Distance36.7 ± 0.2 ly
(11.26 ± 0.07 pc)
Absolute magnitude (MV)−0.30±0.02[6]
Mass1.08±0.06[7] M
Radius25.4±0.2[7] R
Diameter25.4±0.2[7] D
Luminosity170[8] L
Surface gravity (log g)1.66±0.05[7] cgs
Temperature4286±30[7] K
Metallicity [Fe/H]−0.52±0.04[7] dex
Rotational velocity (v sin i)2.4±1.0[6] km/s
[7] Gyr
Other designations
Alramech, Alramech, Abramech, α Boötis, 16 Boötes, BD+19° 2777, GJ 541, HD 124897, HIP 69673, HR 5340, SAO 100944, LHS 48, GCTP 3242.00
Database references
Data sources:
Hipparcos Catalogue,
CCDM (2002),
Bright Star Catalogue (5th rev. ed.),
VizieR catalog entry

Arcturus, also known as Alpha Boötis (α Boötis, abbreviated Alpha Boo, α Boo), is the brightest star in the constellation Boötes, the 3rd brightest in the night sky, and the brightest star in the northern hemisphere. Together with Spica and Denebola (alternatively Regulus depending on the source), Arcturus is part of the Spring Triangle, along with being part of the Great Diamond along with the star Cor Caroli.

Relatively close at 36.7 light-years from the Sun, Arcturus is a red giant of spectral type K0III. Arcturus is an ageing star around 7.1 billion years old that has used up its core hydrogen and moved off the main sequence line; it is 1.08 ± 0.06 times as massive as the Sun and has expanded to 25.4 ± 0.2 times its diameter and is over 170 times brighter. It has probably originated in a dwarf galaxy along with other naked eye red giants.


Optical image of Arcturus (DSS2 / MAST / STScI / NASA)

Based upon an annual parallax shift of 88.83 milliarcseconds as measured by the Hipparcos satellite, Arcturus is 36.7 light-years (11.26 parsecs) from the Sun. The parallax margin of error is 0.54 milliarcseconds, translating to a distance margin of error of ±0.23 light-years (0.069 parsecs).[1] Because of its proximity, Arcturus has a high proper motion, two arcseconds a year, greater than any first magnitude star other than α Centauri.

Arcturus is moving rapidly (122 km/s) relative to the Solar System, and is now almost at its closest point to the Sun. Closest approach will happen in about 4,000 years, when the star will be a few hundredths of a light-year closer to Earth than it is today. (In antiquity, Arcturus was closer to the centre of the constellation.[9]) Arcturus is thought to be an old disk star, and appears to be moving with a group of 52 other such stars, known as the Arcturus stream.[10]

With an absolute magnitude of −0.30 Arcturus is, together with Vega and Sirius, one of the most luminous stars in the Sun's neighborhood. It is about 110 times brighter than the Sun in visible light wavelengths, but this underestimates its strength as much of the light it gives off is in the infrared; total (bolometric) power output is about 180 times that of the Sun. The lower output in visible light is due to a lower efficacy as the star has a lower surface temperature than the Sun. With a near-infrared J band magnitude of −2.2, only Betelgeuse (−2.9) and R Doradus (−2.6) are brighter.

Arcturus is an evolved red giant star with a stellar classification of K0 III. As the brightest K-type giant in the sky, it was the subject of an atlas of its visible spectrum, made from photographic spectra taken with the coudé spectrograph of the Mt. Wilson 2.5m telescope published in 1968,[11] a key reference work for stellar spectroscopy. Subsequent spectral atlases[12][13][14] with greater wavelength coverage and superior signal-to-noise ratio made with digital detectors have supplanted the older work, but the Arcturus spectrum remains an important standard for stellar spectroscopy.

As a single star, the mass of Arcturus cannot be measured directly, but models suggest it is slightly larger than that of the Sun. Evolutionary matching to the observed physical parameters gives a mass of 1.08 ± 0.06 M,[7] while the oxygen isotope ratio for a first dredge-up star gives a mass of 1.2 M.[15] The star displays magnetic activity that is heating the coronal structures, and it undergoes a solar-type magnetic cycle with a duration that is probably less than 14 years. A weak magnetic field has been detected in the photosphere with a strength of around half a gauss. The magnetic activity appears to lie along four latitudes and is rotationally-modulated.[16]

Arcturus is estimated to be around 6 billion to 8.5 billion years old,[7] but there is some uncertainty about its evolutionary status.[17] Based upon the color characteristics of Arcturus, it is currently ascending the red-giant branch and will continue to do so until it accumulates a large enough degenerate helium core to ignite the helium flash.[7] It has likely exhausted the hydrogen from its core and is now in its active hydrogen shell burning phase. However, Charbonnel et al. (1998) placed it slightly above the horizontal branch, and suggested it has already completed the helium flash stage.[17]


As one of the brightest stars in the sky, Arcturus has been the subject of a number of studies in the emerging field of asteroseismology. Belmonte and colleagues carried out a radial velocity (Doppler shift of spectral lines) study of the star in April and May 1988, which showed variability with a frequency of the order of a few microhertz (μHz), the highest peak corresponding to 4.3 μHz (2.7 days) with an amplitude of 60 ms−1, with a frequency separation of c. 5 μHz. They suggested that the most plausible explanation for the variability of Arcturus is stellar oscillations.[18]

Asteroseismological measurements allow direct calculation of the mass and radius, giving values of 0.8 ± 0.2 M and 27.9 ± 3.4 D. This form of modelling is still relatively inaccurate, but a useful check on other models.[19]

Element abundance

Astronomers term "metals" those elements with higher atomic numbers than helium. Arcturus has an enrichment of alpha elements relative to iron but only about a third of solar metallicity. Arcturus is possibly a Population II star.[20]

Possible planetary system

Hipparcos also suggested that Arcturus is a binary star, with the companion about twenty times dimmer than the primary and orbiting close enough to be at the very limits of humans' current ability to make it out. Recent results remain inconclusive, but do support the marginal Hipparcos detection of a binary companion.[21]

In 1993, radial velocity measurements of Aldebaran, Arcturus and Pollux showed that Arcturus exhibited a long-period radial velocity oscillation, which could be interpreted as a substellar companion. This substellar object would be nearly 12 times the mass of Jupiter and be located roughly at the same orbital distance from Arcturus as the Earth is from the Sun, at 1.1 astronomical units. 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. So far no substellar companion has been confirmed.[22]

Other names

In Arabic

In Arabic, Arcturus is one of two stars called al-simāk "the uplifted ones" (the other is Spica). Arcturus is specified as السماك الرامح as-simāk ar-rāmiħ "the uplifted one of the lancer". The term Al Simak Al Ramih has appeared in Al Achsasi Al Mouakket catalogue (translated into Latin as Al Simak Lanceator).[23]

This has been variously romanized in the past, leading to obsolete variants such as Aramec and Azimech. For example, the name Alramih is used in Geoffrey Chaucer's A Treatise on the Astrolabe (1391). Another Arabic name is Haris-el-sema, from حارس السماء ħāris al-samā’ "the keeper of heaven".[24][25][26] or حارس الشمال ħāris al-shamāl’ "the keeper of north".[27]

Arcturus was once again called by its classical name from the Renaissance onwards.[28]


In Chinese astronomy, Arcturus is called Da Jiao (Chinese: 大角; pinyin: Dàjiǎo; literally: "great horn"), because it is the brightest star in the Chinese constellation called Jiao Xiu (Chinese: 角宿; pinyin: Jiǎo Xiǔ; literally: "horn star"). Later it become a part of another constellation Kang Xiu (Chinese: 亢宿; pinyin: Kàng Xiǔ).

In Indian Astrology or Vedic Astrology or Sidereal Astrology, Arcturus is called Swati which is a word meaning "very beneficent" derived from the language Sanskrit. It is the eponymous star of one of the nakshatras (lunar mansions) of Hindu astrology.

In Indonesia, Arcturus is called Bintang Biduk (star of boat).[citation needed]

In Japan, Arcturus is called Mugi-boshi (麦星), meaning star of wheat.[citation needed]

Other languages

The Wotjobaluk Koori people of southeastern Australia knew Arcturus as Marpean-kurrk, mother of Djuit (Antares) and another star in Bootes, Weet-kurrk[29] (Muphrid).[30] Its appearance in the north signified the arrival of the larvae of the wood ant (a food item) in spring. The beginning of summer was marked by the star's setting with the Sun in the west and the disappearance of the larvae.[29] The people of Milingimbi Island in Arnhem Land saw Arcturus and Muphrid as man and woman, and took the appearance of Arcturus at sunrise as a sign to go and harvest rakia or spikerush.[31]:24,69,112 The Wailwun of northern New South Wales knew Arcturus as Guembila "red".[31]:84

In Inuit astronomy, Arcturus is called the Old Man (Uttuqalualuk in Inuit languages) and The First Ones (Sivulliik in Inuit languages).[32]

The Mi'kmaq of eastern Canada saw Arcturus as Kookoogwéss, the owl.[33]

Arcturus had several names that described its significance to indigenous Polynesians. In the Society Islands, Arcturus, called Ana-tahua-taata-metua-te-tupu-mavae ("a pillar to stand by"), was one of the ten "pillars of the sky", bright stars that represented the ten heavens of the Tahitian afterlife.[34] In Hawaii, the pattern of Boötes was called Hoku-iwa, meaning "stars of the frigatebird". This constellation marked the path for Hawaiiloa on his return to Hawaii from the South Pacific Ocean.[35] The Hawaiians called Arcturus Hoku-leʻa.[36] It was equated to the Tuamotuan constellation Te Kiva, meaning "frigatebird", which could either represent the figure of Boötes or just Arcturus.[37] However, Arcturus may instead be the Tuamotuan star called Turu.[38] The Hawaiian name for Arcturus as a single star was likely Hoku-leʻa, which means "star of gladness", or "clear star".[39] In the Marquesas Islands, Arcturus was probably called Tau-tou and was the star that ruled the month approximating January. The Māori and Moriori called it Tautoru, a variant of the Marquesan name and a name shared with Orion's Belt.[40]

In culture

As one of the brightest stars in the sky, Arcturus has been significant to observers since antiquity.

Historical cultures

Prehistoric Polynesian navigators knew Arcturus as Hōkūleʻa, the "Star of Joy". Arcturus is the zenith star of the Hawaiian Islands. Using Hōkūleʻa and other stars, the Polynesians launched their double-hulled canoes from Tahiti and the Marquesas Islands. Traveling east and north they eventually crossed the equator and reached the latitude at which Arcturus would appear directly overhead in the summer night sky. Knowing they had arrived at the exact latitude of the island chain, they sailed due west on the trade winds to landfall. If Hōkūleʻa could be kept directly overhead, they landed on the southeastern shores of the Big Island of Hawaiʻi. For a return trip to Tahiti the navigators could use Sirius, the zenith star of that island. Since 1976, the Polynesian Voyaging Society's Hōkūleʻa has crossed the Pacific Ocean many times under navigators who have incorporated this wayfinding technique in their non-instrument navigation.

In ancient Mesopotamia, it was linked to the god Enlil, and also known as Shudun, "yoke",[9] or SHU-PA of unknown derivation in the Three Stars Each Babylonian star catalogues and later MUL.APIN around 1100 BC.[41]

In Ancient Rome, the star's celestial activity was supposed to portend tempestuous weather, and a personification of the star acts as narrator of the prologue to Plautus' comedy Rudens (circa 211 BC).[42][43]

In the Hebrew scriptures Arcturus is referred to in Job 38:32.[44]

In the Middle Ages, Arcturus was considered a Behenian fixed star[45] and attributed to the stone Jasper and the plantain herb. Cornelius Agrippa listed its kabbalistic sign Agrippa1531 Alchameth.png under the alternate name Alchameth.

The Karandavyuha sutra, compiled at the end of the 4th century or beginning of the 5th century, names one of Avalokiteshvara's meditative absorptions as "The face of Arcturus".[46]

Modern cultures

Arcturus achieved fame when its light was rumored to be the mechanism used to open the 1933 Chicago World's Fair. The star was chosen as it was thought that light from Arcturus had started its journey at about the time of the previous Chicago World's Fair in 1893 (at 36.7 light-years away, and the light actually started in 1896.[47]

The star is featured in the 1977 documentary film Powers of Ten, in which it is seen when a camera zooms from Earth to the whole of the known universe.

See also

Explanatory notes


  1. 1.0 1.1 1.2 1.3 van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–64. arXiv:0708.1752. Bibcode 2007A&A...474..653V. doi:10.1051/0004-6361:20078357.
  2. 2.0 2.1 2.2 2.3 2.4 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.
  3. Gray, R. O.; Corbally, C. J.; Garrison, R. F.; McFadden, M. T.; Robinson, P. E. (2003). "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I". The Astronomical Journal 126 (4): 2048. arXiv:astro-ph/0308182. Bibcode 2003AJ....126.2048G. doi:10.1086/378365.
  4. Massarotti, Alessandro; Latham, David W.; Stefanik, Robert P.; Fogel, Jeffrey (2008). "Rotational and Radial Velocities for a Sample of 761 HIPPARCOS Giants and the Role of Binarity". The Astronomical Journal 135: 209. Bibcode 2008AJ....135..209M. doi:10.1088/0004-6256/135/1/209.
  5. 5.0 5.1 Lua error in Module:Citation/CS1 at line 379: attempt to call method 'match' (a nil value).
  6. 6.0 6.1 Carney, Bruce W. et al. (March 2008). "Rotation and Macroturbulence in Metal-Poor Field Red Giant and Red Horizontal Branch Stars". The Astronomical Journal 135 (3): 892–906. arXiv:0711.4984. Bibcode 2008AJ....135..892C. doi:10.1088/0004-6256/135/3/892.
  7. 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8 I. Ramírez; C. Allende Prieto (December 2011). "Fundamental Parameters and Chemical Composition of Arcturus". The Astrophysical Journal 743 (2): 135. arXiv:1109.4425. Bibcode 2011ApJ...743..135R. doi:10.1088/0004-637X/743/2/135.
  8. Schröder, K.-P.; Cuntz, M. (April 2007). "A critical test of empirical mass loss formulas applied to individual giants and supergiants". Astronomy and Astrophysics 465 (2): 593–601. arXiv:astro-ph/0702172. Bibcode 2007A&A...465..593S. doi:10.1051/0004-6361:20066633.
  9. 9.0 9.1 Rogers, John H. (1998). "Origins of the Ancient Constellations: II. The Mediterranean Traditions". Journal of the British Astronomical Association 108 (2): 79–89. Bibcode 1998JBAA..108...79R.
  10. Ramya, P.; Reddy, Bacham E.; Lambert, David L. (2012). "Chemical compositions of stars in two stellar streams from the Galactic thick disc". Monthly Notices of the Royal Astronomical Society 425 (4): 3188. arXiv:1207.0767. Bibcode 2012MNRAS.425.3188R. doi:10.1111/j.1365-2966.2012.21677.x.
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  15. Abia, C.; Palmerini, S.; Busso, M.; Cristallo, S. (2012). "Carbon and oxygen isotopic ratios in Arcturus and Aldebaran. Constraining the parameters for non-convective mixing on the red giant branch". Astronomy & Astrophysics 548: A55. arXiv:1210.1160. Bibcode 2012A&A...548A..55A. doi:10.1051/0004-6361/201220148.
  16. Sennhauser, C.; Berdyugina, S. V. (May 2011). "First detection of a weak magnetic field on the giant Arcturus: remnants of a solar dynamo?". Astronomy & Astrophysics 529: 6. Bibcode 2011A&A...529A.100S. doi:10.1051/0004-6361/201015445. A100.
  17. 17.0 17.1 Pavlenko, Ya. V. (September 2008). "The carbon abundance and 12C/13C isotopic ratio in the atmosphere of Arcturus from 2.3 µm CO bands". Astronomy Reports 52 (9): 749–759. arXiv:0807.3667. Bibcode 2008ARep...52..749P. doi:10.1134/S1063772908090060.
  18. Belmonte, J. A.; Jones, A. R.; Palle, P. L.; Roca Cortes, T. (1990). "Acoustic oscillations in the K2 III star Arcturus". Astrophysics and Space Science 169 (1–2): 77–84. Bibcode 1990Ap&SS.169...77B. doi:10.1007/BF00640689. ISSN 0004-640X.
  19. Kallinger, T.; Weiss, W. W.; Barban, C.; Baudin, F.; Cameron, C.; Carrier, F.; De Ridder, J.; Goupil, M.-J. et al. (2010). "Oscillating red giants in the CoRoT exofield: Asteroseismic mass and radius determination". Astronomy and Astrophysics 509: A77. arXiv:0811.4674. Bibcode 2010A&A...509A..77K. doi:10.1051/0004-6361/200811437.
  20. Cite error: Invalid <ref> tag; no text was provided for refs named schaaf
  21. Verhoelst, T.; Bordé, P. J.; Perrin, G.; Decin, L. et al. (2005). "Is Arcturus a well-understood K giant?". Astronomy & Astrophysics 435: 289. arXiv:astro-ph/0501669. Bibcode 2005A&A...435..289V. doi:10.1051/0004-6361:20042356, and see references therein.
  22. Hatzes, A.; Cochran, W. (August 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.
  23. Knobel, E. B. (June 1895). "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket". Monthly Notices of the Royal Astronomical Society 55: 429. Bibcode 1895MNRAS..55..429K. doi:10.1093/mnras/55.8.429.
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  27. Davis Jr., G. A. (October 3, 1944). "The Pronunciations, Derivations, and Meanings of a Selected List of Star Names". Popular Astronomy LII: 13. Bibcode 1944PA.....52....8D.
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  30. Hamacher, Duane W.; Frew, David J. (2010). "An Aboriginal Australian Record of the Great Eruption of Eta Carinae". Journal of Astronomical History & Heritage 13 (3): 220–34. arXiv:1010.4610. Bibcode 2010JAHH...13..220H.
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  33. Hagar, Stansbury (1900). "The Celestial Bear". The Journal of American Folklore 13 (49): 92–103. doi:10.2307/533799. JSTOR 533799.
  34. Lua error in Module:Citation/CS1 at line 379: attempt to call method 'match' (a nil value).
  35. Makemson 1941, p. 209.
  36. Makemson 1941, p. 280.
  37. Makemson 1941, p. 221.
  38. Makemson 1941, p. 264.
  39. Makemson 1941, p. 210.
  40. Makemson 1941, p. 260.
  41. Rogers, John H. (1998). "Origins of the Ancient Constellations: I. The Mesopotamian Traditions". Journal of the British Astronomical Association 108 (1): 9–28. Bibcode 1998JBAA..108....9R.
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  45. Tyson, Donald; Freake, James (1993), Three Books of Occult Philosophy, Llewellyn Worldwide, ISBN 0-87542-832-0
  46. Lua error in Module:Citation/CS1 at line 379: attempt to call method 'match' (a nil value).
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External links