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Albireo A
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
Right ascension 19h 30m 19h 30m
  43.281s 43.302s
Declination +27° 57′[1] +27° 57′[2]
  34.85″ 34.61″
Apparent magnitude (V) 3.18[3] 5.82[3]
Spectral type K3III[4] B0V[4]
V-R color index 0.92[3] 0.09[3]
Proper motion:  
RA α cos δ)  −7.09[1] mas/yr  5.04[2] mas/yr 
Dec. δ)  −5.63[1] mas/yr  6.48[2] mas/yr 
Parallax (π) 8.46 ± 0.58[5] mas
Distance 390 ± 30 ly
(118 ± 8 pc)
Absolute magnitude (MV) −2.18[3] 0.46[3]
Mass 5[6] M 3.2[6] M
Radius 16[7] R
Luminosity (bolometric) 1200±200[3] L 950±250[3] L
Temperature 4080±10[3] K 30000±100[3] K
Period (P) 213.859 yr
Semimajor axis (a) 0.536
Eccentricity (e) 0.256
Inclination (i) 154.9°
Longitude of node (Ω) 170.4°
Periastron epoch (T) B1997.995
Argument of periastron (ω)
Database references
Other designations
β Cygni A, β1 Cygni, 6 Cygni A, MCA 55 Aac, ADS 12540 A, BD+27 3410, CCDM J19307+2758A, FK5 732, HD 183912/183913, HIP 95947, HR 7417, NSV 12105, SAO 87301, WDS 19307+2758Aa/Ac[5][8][9]

Albireo (β Cyg / β Cygni / Beta Cyg / Beta Cygni) is the fifth brightest star in the constellation Cygnus. Although it has the Bayer designation beta, it is fainter than Gamma Cygni, Delta Cygni, and Epsilon Cygni. Albireo appears to the naked eye to be a single star but can be resolved with a telescope into a double star, consisting of a brighter yellow star (actually a binary system of two stars in orbit) and a fainter blue star. Albireo is cherished by amateur astronomers as a beautiful small telescope object.[6]


Double star


Albireo is approximately 380 light-years (120 pc) away from the Earth. When viewed with the naked eye, Albireo appears to be a single star. However, when viewed with a telescope it readily resolves into a double star, consisting of Albireo A (amber, apparent magnitude 3.1), and Albireo B (blue-green, apparent magnitude 5.1.)[10] Separated by 35 seconds of arc,[11] 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 are orbiting around each other in a physical binary system. If they are, their orbital period is probably at least 100,000 years.[10]

Albireo A

In 1976, component A was itself discovered to be a binary star, using speckle interferometry and the 2.1-meter telescope at the Kitt Peak National Observatory.[9][12] 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.[9] The current angular separation between the components of around 0.4 arcseconds is tantalizingly close to the limit which visual observations through instruments of at least 20" in size can resolve, under very rare perfect seeing conditions.

Albireo B

Albireo B
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Cygnus
Right ascension 19h 30m 45.3954s[13]
Declination +27° 57′ 54.995″[13]
Apparent magnitude (V) 5.09[13]
Spectral type B8Ve[13]
U-B color index -0.30[14]
B-V color index -0.06[13]
Radial velocity (Rv) -18[13] km/s
Proper motion:  
RA α cos δ)  -1.95[13] mas/yr 
Dec. δ)  -0.98[13] mas/yr 
Parallax (π) 8.67 ± 0.65[13] mas
Distance 380 ± 30 ly
(115 ± 9 pc)
Mass 3.7 ± 0.8[15] M
Radius 2.7[16] R
Surface gravity (log g) 4.00 ± 0.15[15]
Luminosity (bolometric) 230 ± 90[15] L
Temperature 13200 ± 600[15] K
Rotation <0.6 days[6]
Age 4×107 to 2×108 [15]y
Position (relative to Albireo A)
Epoch of observation 2006
Angular distance 35.3 [11]
Position angle 54°[11]
Database references
Other designations
β Cygni B, β2 Cygni, 6 Cygni B, STF 4043B, ADS 12540 B, BD+27 3411, CCDM J19307+2758B, HD 183914, HIP 95951, HR 7418, SAO 87302, WDS 19307+2758B[11][13]

Albireo B is a fast-rotating Be star, with an equatorial rotational velocity of at least 250 kilometers per second.[6] Its surface temperature has been spectroscopically estimated to be about 13,200 K.[15]

Names and etymology

Since Cygnus is the swan, and Albireo is located at the head of the swan, Albireo is sometimes called the "beak star".[17] With Deneb, Gamma Cygni, Delta Cygni, and Epsilon Cygni, it forms the asterism called the Northern Cross.[18]

Medieval Arabic-speaking astronomers called Albireo minqār al-dajājah (English: the hen's beak.)[19] Its current name 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.[20] When translated into Latin, this name was thought to refer to the plant Erysimum officinale, and so was translated into a Latin name for this plant, ireo. The phrase ab ireo was later treated as a misprint of an Arabic term and transcribed as al-bireo.[21]

Cultural significance

The University of California at Berkeley's student government, the ASUC senate, officially adopted Albireo as its "official campus star". Renowned UC Berkeley Astronomy professor, Alex Filippenko, had "been showing the binary star to students in his Astronomy 10 class for years"[22] prior to the senate's official recognition, referring to it as the "Cal Star"[23] because UC Berkeley's official colours are blue and gold like Beta Cygni's constituent stars.


  1. ^ a b c HIP 95947, record for component 1, Hipparcos catalogue; CDS ID I/239.
  2. ^ a b c HIP 95947, record for component 2, Hipparcos catalogue; CDS ID I/239.
  3. ^ a b c d e f g h i j 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.
  4. ^ a b Entry, The Washington Double Star Catalog, identifier 19307+2758, discoverer identifier MCA 55. Accessed on line July 9, 2008.
  5. ^ a b CCDM J19307+2758A -- Double or multiple star, database entry, SIMBAD. Accessed on line July 9, 2008.
  6. ^ a b c d e Albireo, Stars, Jim Kaler. Accessed on line July 9, 2008.
  7. ^ Entry, HD 183912, Catalogue of Stellar Diameters (CADARS); CDS ID II/224.
  8. ^ a b 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.
  9. ^ a b c Speckle observations with PISCO in Merate: IV. Astrometric measurements of visual binaries in 2005, M. Scardia et al., Astronomische Nachrichten 329, #1 (2008), pp. 54–68. Bibcode2008AN....329...54S. doi:10.1002/asna.200710834.
  10. ^ a b p. 46, The Monthly Sky Guide, Ian Ridpath, Wil Tirion, Cambridge University Press, 2006, ISBN 0521684358.
  11. ^ a b c d Entry, The Washington Double Star Catalog, identifier 19307+2758, discoverer identifier STFA 43. Accessed on line July 9, 2008.
  12. ^ Speckle interferometric measurements of binary stars. VI, H. A. McAlister and E. M. Hendry, Astrophysical Journal Supplement Series 48 (March 1982), pp. 273–278. Bibcode1982ApJS...48..273M. doi:10.1086/190778.
  13. ^ a b c d e f g h i j HD 183914 -- Emission-line Star, database entry, SIMBAD. Accessed on line July 9, 2008.
  14. ^ 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.
  15. ^ 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.
  16. ^ Entry, HD 183914, Catalogue of Stellar Diameters (CADARS); CDS ID II/224.
  17. ^ p. 416, In Quest of the Universe, Theo Koupelis and Karl F. Kuhn, 5th ed., Sudbury, Massachusetts: Jones & Bartlett Publishers, 2007, ISBN 0763743879.
  18. ^ Northern Cross, entry, The Internet Encyclopedia of Science, David Darling. Accessed on line July 24, 2008.
  19. ^ p. 196, Star-names and Their Meanings, Richard Hinckley Allen, New York, G. E. Stechert, 1899.
  20. ^ p. 24, The names of the stars and constellations compiled from the Latin, Greek and Arabic, W. H. Higgins, Leicester: Samuel Clarke, 1882.
  21. ^ p. 194, Allen.
  22. ^ Accessed online December 28, 2008.
  23. ^ Accessed online December 27, 2008.

External links



Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary




From Arabic, via misunderstandings and mistranslations. The name of the star was originally al-Minhar al-Dajajah, "the hen's beak". Latin scholars misunderstood the name to come from a kind of herb, and translated it into ab ireo ("from ireus"). Later, people considered it as a misprint of an Arabic term, and transcribed it as al-bireo.

Proper noun

Wikipedia has an article on:



  1. (astronomy): A binary star in the constellation Cygnus; Beta (β) Cygni.



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