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Position beta Cyg.png
Albireo's position, lower right corner.
The cross-like figure is the Northern Cross.
The blue line shows the boundaries of the constellation the Swan.
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Cygnus
Albireo Aa
Right ascension 19h 30m 43.286s
Declination +27° 57′ 34.84″[1]
Apparent magnitude (V) 3.18[2]
Albireo Ac
Right ascension 19h 30m 43.295s
Declination +27° 57′ 34.62″[3]
Apparent magnitude (V) 5.82[2]
Albireo B
Right ascension 19h 30m 45.3954s[4]
Declination +27° 57′ 54.995″[4]
Apparent magnitude (V) 5.09[4]
Albireo Aa
Spectral type K2II[5]
B−V color index 1.074[1]
V−R color index 0.92[2]
Albireo Ac
Spectral type B8:p[5]
B−V color index 0.09[3]
V−R color index 0.09[2]
Albireo B
Spectral type B8Ve[4]
U−B color index -0.30[6]
B−V color index -0.06[4]
Radial velocity (Rv) -24.07 km/s
Proper motion (μ) RA: -7.17 mas/yr
Dec.: -6.15 mas/yr
Parallax (π) 7.51 ± 0.33[7][a] mas
Distance 430 ± 20 ly
(133 ± 6 pc)
Albireo Aa
Absolute magnitude (MV) −2.45[5]
Albireo Ac
Absolute magnitude (MV) −0.25[5]
Radial velocity (Rv) -18[4] km/s
Proper motion (μ) RA: -1.95[4] mas/yr
Dec.: -0.98[4] mas/yr
Parallax (π) 8.16 ± 0.25[4][a] mas
Distance 400 ± 10 ly
(123 ± 4 pc)
Orbit (Aa/Ac)[8]
Period (P) 213.859 yr
Semi-major axis (a) 0.536
Eccentricity (e) 0.256
Inclination (i) 154.9°
Longitude of the node (Ω) 170.4°
Periastron epoch (T) B1997.995
Argument of periastron (ω)
Albireo Aa
Mass 14.52[9] M
Luminosity (bolometric) 1,200 ± 200[2] L
Surface gravity (log g) 2.0[10] cgs
Temperature 4,270[10] K
Metallicity [Fe/H] −0.1[10] dex
Rotational velocity (v sin i) 1.4[10] km/s
Albireo Ac
Mass 3.84[9] M
Luminosity (bolometric) 950 ± 250[2] L
Temperature ~12,000[5]–30,000±100[2] K
Albireo B
Mass 3.7 ± 0.8[11] M
Radius 2.59[12] R
Luminosity (bolometric) 230 ± 90[11] L
Surface gravity (log g) 4.00 ± 0.15[11] cgs
Temperature 13,200 ± 600[11] K
Age 100[11] Myr
Position (relative to Albireo A)
Component Albireo B
Epoch of observation 2006
Angular distance 35.3 [13]
Position angle 54° [13]
Other designations
β Cygni, 6 Cygni, ADS 12540, CCDM J19307+2758, WDS 19307+2758[7][8][14]
AlbireoA: β¹ Cygni, BD+27 3410, HR 7417, HD 183912/183913, HIP 95947, SAO 87301, FK5 732, MCA 55 Aac, NSV 12105
AlbireoB: β² Cygni, STF 4043B, BD+27 3411, HD 183914, HIP 95951, HR 7418, SAO 87302[4]
Database references
SIMBAD Albireo A
Albireo B

Albireo is the traditional name for the double star also designated Beta Cygni (β Cygni, abbreviated Beta Cyg, β Cyg), although the International Astronomical Union now regards the name as only applying to the brightest component.[15] Despite being designated 'beta', it is fainter than Gamma Cygni, Delta Cygni, and Epsilon Cygni and is the fifth-brightest point of light in the constellation of Cygnus. Appearing to the naked eye to be a single star of magnitude 3, viewing through even a low-magnification telescope resolves it into its two components. The brighter yellow star (actually itself a very close binary system) makes a striking colour contrast with its fainter blue companion.[16]


β Cygni (Latinised to Beta Cygni) is the system's Bayer designation. The brighter of the two components is designated β¹ Cygni or Beta Cygni A and the fainter β² Cygni or Beta Cygni B.

The system's traditional name Albireo is a result of misunderstanding and mistranslation. It is thought that it originated in the Greek name ornis for the constellation of Cygnus, which became urnis in Arabic.[17] When translated into Latin, this name was thought to refer to the Greek name Erysimon for the plant Sisymbrium officinale (which in Latin is ireo), and so was described in Latin in the Arabo-Latin Almagest of 1515 as "Eurisim: et est volans; et jam vocatur gallina. et dicitur eurisim quasi redolens ut lilium ab ireo" ("Eurisim: and it is the flyer, and now it is called the hen, and it is called Eurisim, as if redolent like the lily from the 'ireo'"), via a confusion between ireo and the scented flower Iris florentina. This was variously miscopied, until "ab ireo" was treated as a miscopy of an Arabic term and changed into al-bireo.[18] [19]

In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[20] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[21] included a table of the first two batches of names approved by the WGSN; which included Albireo for β¹ Cygni. It is now so entered in the IAU Catalog of Star Names.[15]

Medieval Arabic-speaking astronomers called Beta Cygni minqār al-dajājah (English: the hen's beak).[22] The term minqār al-dajājah (منقار الدجاجة) or Menchir al Dedjadjet appeared in the catalogue of stars in the Calendarium of Al Achsasi Al Mouakket, which was translated into Latin as Rostrum Gallinae, meaning the hen's beak.[23]

Since Cygnus is the swan, and Beta Cygni is located at the head of the swan, it is sometimes called the "beak star".[24] With Deneb, Gamma Cygni (Sadr), Delta Cygni, and Epsilon Cygni (Gienah), it forms the asterism called the Northern Cross.[25]


Albireo A and B (Hunter Wilson)

Beta Cygni is about 430 light-years (130 pc)[a] away from the Sun.

Visual companions[edit]

When viewed with the naked eye, Albireo appears to be a single star. However, in a telescope it readily resolves into a double star consisting of β Cygni A (amber, apparent magnitude 3.1), and β Cygni B (blue-green, apparent magnitude 5.1).[26] Separated by 35 seconds of arc,[13] the two components provide one of the best contrasting double stars in the sky due to their different colors.

It is not known whether the two components β Cygni A and B are orbiting around each other in a physical binary system, or if they are merely an optical double. If they are a physical binary, their orbital period is probably at least 100,000 years.[26] Some experts, however, support the optical double argument, based on observations that suggest different proper motions for the components, which implies they're unrelated.[27]

There are a further 10 faint companions listed in the Washington Double Star catalogue, all fainter than magnitude 10. Only one is closer to the primary than Albireo B, with the others up to 142" away.[8]

Albireo A[edit]

The spectrum of Beta Cygni A was found to be composite when it was observed as part of the Henry Draper Memorial project in the late 19th century, leading to the supposition that it was itself double.[28] This was supported by observations from 1898 to 1918 which showed that it had a varying radial velocity.[29] In 1923, the two components were identified in the Henry Draper Catalogue as HD 183912 and HD 183913.[30][31]

In 1978, speckle interferometry observations using the 1.93m telescope at the Haute-Provence Observatory resolved a companion at 0.125". This observation was published in 1980,[32] and the companion is referred to as component Ab in the Washington Double Star Catalog.[8]

In 1976 speckle interferometry was used to resolve a companion using the 2.1-meter telescope at the Kitt Peak National Observatory. It was measured at a separation of 0.44", and it is specifically noted that the observation was inconsistent with the Haute-Provence observations and hence not of the same star.[14][33] Although these observations pre-dated those at Haute-Provence, they were not published until 1982 and this component is designated Ac in the Washington Double Star Catalog.[8] It is designated as component C in the Catalog of Components of Double and Multiple Stars,[34] not to be confused with component C in the Washington Double Star Catalog which is a faint optical companion.[8] An orbit for the pair has since been computed using interferometric measurements, but as only approximately a quarter of the orbit has been observed, the orbital parameters must be regarded as preliminary. The period of this orbit is 214 years.[14]

The status of the two possible companions is still not clarified.[35] One set of observations reports barely resolving two components, but there has not been confirmation of this.[36] Observations of Albireo assuming the spectrum is a composite of two stars derive a late B spectral type for the companion,[37], for example B8.[5] Adaptive optics measurements of the companion are best modelled by a B0V spectrum for the companion with an apparent magnitude of 5.85.[2] Different assumptions about the spectral type of the companion lead to wildly different physical properties, for example an effective temperature of either 12,000 K or 30,000 K.[5][2]

The diameter of the primary K-type giant star has been measured using interferometry. A uniform disk of approximately 4.5 mas was measured at optical and near-infrared wavelengths, and a limb-darkened diameter of 4.834 mas was calculated, equivalent to a radius of 69 R at a distance of 133 pc.[38]

Albireo B[edit]

β Cygni B is a fast-rotating Be star, with an equatorial rotational velocity of at least 250 kilometers per second.[16] Its surface temperature has been spectroscopically estimated to be about 13,200 K.[11]

β Cygni B has been reported to be a very close double,[35] but the observations appear to have been incorrect.[8]


Albireo (AK-90) was a United States Navy Crater class cargo ship named after the star.


  1. ^ a b c The primary and secondary have different formal Hipparchos parallaxes. They are thought to be physically related and so at the same distance from Earth in astronomical terms, hence one or both derived distances are somewhat in error.


  1. ^ a b [1], Hipparcos catalogue; CDS.
  2. ^ a b c d e f g h i Binary Star Differential Photometry Using the Adaptive Optics System at Mount Wilson Observatory, Theo ten Brummelaar, Brian D. Mason, et al., Astronomical Journal 119, #5 (May 2000), pp. 2403–2414. doi:10.1086/301338. Bibcode2000AJ....119.2403T. See tables 4, 5, 6, and 8. Luminosity from Lbol=102(4.75−Mbol)/5.
  3. ^ a b [2], Hipparcos catalogue; CDS.
  4. ^ a b c d e f g h i j HD 183914 -- Emission-line Star, database entry, SIMBAD. Accessed on line July 9, 2008.
  5. ^ a b c d e f g Ginestet, N.; Carquillat, J. M. (2002). "Spectral Classification of the Hot Components of a Large Sample of Stars with Composite Spectra, and Implication for the Absolute Magnitudes of the Cool Supergiant Components". The Astrophysical Journal Supplement Series. 143 (2): 513. Bibcode:2002ApJS..143..513G. doi:10.1086/342942. 
  6. ^ UBV observations of visual double stars, T. E. Lutz, Publications of the Astronomical Society of the Pacific 83 (August 1971), pp. 488–490. Bibcode1971PASP...83..488L.
  7. ^ a b NAME ALBIREO -- Star in double system , database entry, SIMBAD. Accessed on line July 9, 2008.
  8. ^ a b c d e f g Entry, WDS identifier 19307+2758, Sixth Catalog of Orbits of Visual Binary Stars, William I. Hartkopf & Brian D. Mason, U.S. Naval Observatory. Accessed on line July 9, 2008. (19307+2758)
  9. ^ a b Tokovinin, A. A. (1997). "MSC - a catalogue of physical multiple stars". A & A Supplement series. 124: 75. Bibcode:1997A&AS..124...75T. doi:10.1051/aas:1997181. 
  10. ^ a b c d Lèbre, A.; De Laverny, P.; Do Nascimento, J. D.; De Medeiros, J. R. (2006). "Lithium abundances and rotational behavior for bright giant stars". Astronomy and Astrophysics. 450 (3): 1173. Bibcode:2006A&A...450.1173L. doi:10.1051/0004-6361:20053485. 
  11. ^ a b c d e f Table 1, Physical Parameters of Southern B- and Be-Type Stars, R. S. Levenhagen and N. V. Leister, The Astronomical Journal 127, #2 (February 2004), pp. 1176–1180, doi:10.1086/381063, Bibcode2004AJ....127.1176L.
  12. ^ Fracassini, Massimo; Gilardoni, Giorgio; Pasinetti, Laura E. (1973). "Apparent diameters of 172 B5V-A5V stars of the Catalogue of Geneva Observatory". Astrophysics and Space Science. 22: 141. Bibcode:1973Ap&SS..22..141F. doi:10.1007/BF00642829. 
  13. ^ a b c Entry, The Washington Double Star Catalog, identifier 19307+2758, discoverer identifier STFA 43. Accessed on line July 9, 2008. Archived 8 September 2008 at the Wayback Machine.
  14. ^ a b c Scardia, M.; Prieur, J.-L.; Pansecchi, L.; Argyle, R.W.; Sala, M.; Basso, S.; Ghigo, M.; Koechlin, L.; Aristidi, E. (2008). "Speckle observations with PISCO in Merate: IV. Astrometric measurements of visual binaries in 2005". Astronomische Nachrichten. 329: 54. Bibcode:2008AN....329...54S. doi:10.1002/asna.200710834. 
  15. ^ a b "IAU Catalog of Star Names". Retrieved 28 July 2016. 
  16. ^ a b Albireo, Stars, Jim Kaler. Accessed on line October 23, 2013.
  17. ^ p. 24, The names of the stars and constellations compiled from the Latin, Greek and Arabic, W. H. Higgins, Leicester: Samuel Clarke, 1882.
  18. ^ p. 194, Allen.
  19. ^*.html
  20. ^ "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016. 
  21. ^ "Bulletin of the IAU Working Group on Star Names, No. 1" (PDF). Retrieved 28 July 2016. 
  22. ^ p. 196, Star-names and Their Meanings, Richard Hinckley Allen, New York, G. E. Stechert, 1899.
  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 (8): 429. Bibcode:1895MNRAS..55..429K. doi:10.1093/mnras/55.8.429. 
  24. ^ p. 416, In Quest of the Universe, Theo Koupelis and Karl F. Kuhn, 5th ed., Sudbury, Massachusetts: Jones & Bartlett Publishers, 2007, ISBN 0-7637-4387-9.
  25. ^ Northern Cross, entry, The Internet Encyclopedia of Science, David Darling. Accessed on line July 24, 2008.
  26. ^ a b p. 46, The Monthly Sky Guide, Ian Ridpath, Wil Tirion, Cambridge University Press, 2006, ISBN 0-521-68435-8.
  27. ^ Bob King (September 21, 2016). "Will the Real Albireo Please Stand Up?". Sky and Telescope. Retrieved October 14, 2016. 
  28. ^ Maury, Antonia C.; Pickering, Edward C. (1897). "Spectra of bright stars photographed with the 11-inch Draper Telescope as part of the Henry Draper Memorial". Annals of Harvard College Observatory. 28: 1. Bibcode:1897AnHar..28....1M. 
  29. ^ Campbell, W. W. (1919). "The Variable Velocity of β Cygni". Publications of the Astronomical Society of the Pacific. 31: 38. Bibcode:1919PASP...31...38C. doi:10.1086/122807. 
  30. ^ "". Retrieved 2017-06-11. 
  31. ^ Cannon, Annie Jump; Pickering, Edward Charles (1923). "The Henry Draper catalogue : 19h and 20h". Annals of the Astronomical Observatory of Harvard College ; v. 98. 98. Bibcode:1923AnHar..98....1C. . See note re HD 183912,3,4 on this page.
  32. ^ Bonneau, D.; Foy, R. (1980). "Speckle interferometric observations of binary systems with the Haute-Provence 1.93 M telescope". Astronomy and Astrophysics. 86: 295. Bibcode:1980A&A....86..295B. 
  33. ^ McAlister, H. A.; Hendry, E. M. (1982). "Speckle interferometric measurements of binary stars. VI". The Astrophysical Journal Supplement Series. 48: 273. Bibcode:1982ApJS...48..273M. doi:10.1086/190778. 
  34. ^ Dommanget, J.; Nys, O. (1994). "Catalogue des composantes d'etoiles doubles et multiples (CCDM) premiere edition - Catalogue of the components of double and multiple stars (CCDM) first edition". Com. de l'Observ. Royal de Belgique. 115: 1. Bibcode:1994CoORB.115....1D. 
  35. ^ a b Roberts, Lewis C.; Turner, Nils H.; Ten Brummelaar, Theo A. (2007). "Adaptive Optics Photometry and Astrometry of Binary Stars. II. A Multiplicity Survey of B Stars". The Astronomical Journal. 133 (2): 545. Bibcode:2007AJ....133..545R. doi:10.1086/510335. 
  36. ^ Prieur, J.-L.; Koechlin, L.; Ginestet, N.; Carquillat, J.-M.; Aristidi, E.; Scardia, M.; Arnold, L.; Avila, R.; Festou, M. C.; Morel, S.; Pérez, J.-P. (2002). "Speckle Observations of Composite Spectrum Stars with PISCO in 1993-1998". The Astrophysical Journal Supplement Series. 142: 95. Bibcode:2002ApJS..142...95P. doi:10.1086/341094. 
  37. ^ Skiff, B. A. (2014). "VizieR Online Data Catalog: Catalogue of Stellar Spectral Classifications (Skiff, 2009-2016)". VizieR On-line Data Catalog: B/mk. Originally published in: Lowell Observatory (October 2014). 1. Bibcode:2014yCat....1.2023S. 
  38. ^ Mozurkewich, D.; Armstrong, J. T.; Hindsley, R. B.; Quirrenbach, A.; Hummel, C. A.; Hutter, D. J.; Johnston, K. J.; Hajian, A. R.; Elias Ii, Nicholas M.; Buscher, D. F.; Simon, R. S. (2003). "Angular Diameters of Stars from the Mark III Optical Interferometer". The Astronomical Journal. 126 (5): 2502. doi:10.1086/378596. 

Further reading[edit]

  • Webb, T. W.; McAlister, H. A.; Worley, C. E.; Burnham, S. W.; Aitken, R. G. (1980). "Albireo as a Triple Star". Sky and Telescope. 59: 210. Bibcode:1980S&T....59..210W. 

External links[edit]