Epoch J2000.0 Equinox J2000.0 (ICRS)
|Right ascension||19h 30m||19h 30m|
|Declination||+27° 57′||+27° 57′|
|Apparent magnitude (V)||3.18||5.82|
|B-V color index||1.074||0.09|
|V-R color index||0.92||0.09|
|Radial velocity (Rv)||-24.07 km/s|
|RA (μα cos δ)||-7.17 mas/yr|
|Dec. (μδ)||-6.15 mas/yr|
|Parallax (π)||7.51 ± 0.33[a] mas|
|Distance||430 ± 20 ly
(133 ± 6 pc)
|Absolute magnitude (MV)||−2.45||−0.25|
|Mass||5 M☉||3.2 M☉|
|Radius||70 R☉||3.5 R☉|
|Luminosity (bolometric)||1,200 L☉||230 L☉|
|Temperature||4,080±10 K||~12,000 K|
|Period (P)||213.859 yr|
|Semimajor axis (a)||0.536″|
|Longitude of node (Ω)||170.4°|
|Periastron epoch (T)||B1997.995|
|Argument of periastron (ω)
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 of magnitude 3 but through a telescope, even low magnification views resolve it into a double star. The brighter yellow star (actually itself a very close binary system) makes a striking colour contrast with its fainter blue companion star.
Double star 
Albireo is about 430 light-years (130 pc)[a] away from the Earth. When viewed with the naked eye, it appears to be a single star. However, in 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). Separated by 35 seconds of arc, 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.
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. The pair is designated as components Aa/Ac in the Washington Double Star Catalog. 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 213 years. The current angular separation between the components is around 0.4 arcseconds, too close to be visually resolved except with instruments of at least 20" in aperture with exceptionally stable atmospheric conditions.
Albireo B 
Epoch J2000.0 Equinox J2000.0 (ICRS)
|Right ascension||19h 30m 45.3954s|
|Declination||+27° 57′ 54.995″|
|Apparent magnitude (V)||5.09|
|U-B color index||-0.30|
|B-V color index||-0.06|
|Radial velocity (Rv)||-18 km/s|
|RA (μα cos δ)||-1.95 mas/yr|
|Dec. (μδ)||-0.98 mas/yr|
|Parallax (π)||8.16 ± 0.25[a] mas|
|Distance||400 ± 10 ly
(123 ± 4 pc)
|Mass||3.7 ± 0.8 M☉|
|Surface gravity (log g)||4.00 ± 0.15|
|Luminosity (bolometric)||230 ± 90 L☉|
|Temperature||13200 ± 600 K|
|Age||4×107 to 2×108 y|
|Position (relative to Albireo A)|
|Epoch of observation||2006|
|Angular distance||35.3″ |
Albireo B is a fast-rotating Be star, with an equatorial rotational velocity of at least 250 kilometers per second. Its surface temperature has been spectroscopically estimated to be about 13,200 K.
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". With Deneb, Gamma Cygni, Delta Cygni, and Epsilon Cygni, it forms the asterism called the Northern Cross.
Medieval Arabic-speaking astronomers called Albireo minqār al-dajājah (English: the hen's beak). 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. 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.
The term minqār al-dajājah (منقار ألدجاجة) 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 Gallinǣ, meaning the hen's beak.
- The primary and secondary have different formal Hipparchos parallaxes. They are thought to be physically related and so at at the same distance from Earth in astronomical terms, hence one or both derived distances are somewhat in error.
- , Hipparcos catalogue; CDS.
- , Hipparcos catalogue; CDS.
- 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. Bibcode: 2000AJ....119.2403T. See tables 4, 5, 6, and 8. Luminosity from Lbol=102(4.75−Mbol)/5.
- 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. doi:10.1086/342942.
- NAME ALBIREO -- Star in double system , database entry, SIMBAD. Accessed on line July 9, 2008.
- Albireo, Stars, Jim Kaler. Accessed on line July 9, 2008.
- 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)
- 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. Bibcode: 2008AN....329...54S. doi:10.1002/asna.200710834.
- p. 46, The Monthly Sky Guide, Ian Ridpath, Wil Tirion, Cambridge University Press, 2006, ISBN 0-521-68435-8.
- 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
- Speckle interferometric measurements of binary stars. VI, H. A. McAlister and E. M. Hendry, Astrophysical Journal Supplement Series 48 (March 1982), pp. 273–278. Bibcode: 1982ApJS...48..273M. doi:10.1086/190778.
- HD 183914 -- Emission-line Star, database entry, SIMBAD. Accessed on line July 9, 2008.
- UBV observations of visual double stars, T. E. Lutz, Publications of the Astronomical Society of the Pacific 83 (August 1971), pp. 488–490. Bibcode: 1971PASP...83..488L.
- 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, Bibcode: 2004AJ....127.1176L.
- Entry, HD 183914, Catalogue of Stellar Diameters (CADARS); CDS ID II/224.
- 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.
- Northern Cross, entry, The Internet Encyclopedia of Science, David Darling. Accessed on line July 24, 2008.
- p. 196, Star-names and Their Meanings, Richard Hinckley Allen, New York, G. E. Stechert, 1899.
- p. 24, The names of the stars and constellations compiled from the Latin, Greek and Arabic, W. H. Higgins, Leicester: Samuel Clarke, 1882.
- p. 194, Allen.
- 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.
- Albireo as a Triple Star
- Photo by Richard Yandrick; August 30, 2005
- A picture of Albireo by Stefan Seip
- NightSkyInfo.com - Albireo
- Albireo at Alcyone Software's Star Data Pages
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