Albireo
 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″ |
| Apparent magnitude (V) | 3.18 |
| Albireo Ac | |
| Right ascension | 19h 30m 43.295s |
| Declination | +27° 57′ 34.62″ |
| Apparent magnitude (V) | 5.82 |
| Albireo B | |
| Right ascension | 19h 30m 45.3954s |
| Declination | +27° 57′ 54.995″ |
| Apparent magnitude (V) | 5.09 |
| Characteristics | |
| Albireo Aa | |
| Spectral type | K2II |
| B−V color index | 1.074 |
| V−R color index | 0.92 |
| Albireo Ac | |
| Spectral type | B8:p |
| B−V color index | 0.09 |
| V−R color index | 0.09 |
| Albireo B | |
| Spectral type | B8Ve |
| U−B color index | -0.30 |
| B−V color index | -0.06 |
| Astrometry | |
| Radial velocity (Rv) | -24.07 km/s |
| Proper motion (μ) |
RA: -7.17 mas/yr Dec.: -6.15 mas/yr |
| Parallax (π) | 7.51 ± 0.33mas |
| Distance | 430 ± 20 ly (133 ± 6 pc) |
| Albireo Aa | |
| Absolute magnitude (MV) | −2.45 |
| Albireo Ac | |
| Absolute magnitude (MV) | −0.25 |
| AlbireoB | |
| Radial velocity (Rv) | -18 km/s |
| Proper motion (μ) |
RA: -1.95 mas/yr Dec.: -0.98 mas/yr |
| Parallax (π) | 8.16 ± 0.25mas |
| Distance | 400 ± 10 ly (123 ± 4 pc) |
| Orbit (Aa/Ac) | |
| 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) (secondary) |
39.4° |
| Details | |
| Albireo Aa | |
| Mass | 5 M☉ |
| Radius | 70 R☉ |
| Luminosity (bolometric) | 1,200 L☉ |
| Temperature | 4,080±10 K |
| Albireo Ac | |
| Mass | 3.2 M☉ |
| Radius | 3.5 R☉ |
| Luminosity (bolometric) | 230 L☉ |
| Temperature | ~12,000 K |
| AlbireoB | |
| Mass | 3.7 ± 0.8 M☉ |
| Radius | 2.7 R☉ |
| Luminosity (bolometric) | 230 ± 90 L☉ |
| Surface gravity (log g) | 4.00 ± 0.15 cgs |
| Temperature | 13200 ± 600 K |
| Rotation | <0.6 days |
| Age | 4×107 to 2×108 years |
| Position (relative to Albireo A) | |
| Component | AlbireoB |
| Epoch of observation | 2006 |
| Angular distance | 35.3″ |
| Position angle | 54° |
| Other designations | |
| 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 | |
| Database references | |
| SIMBAD | AlbireoA data |
| AlbireoB data2 | |
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. 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.
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. When translated into Latin, this name was thought to refer to the Greek name Erysimon for the plant Sisymbrium officinale (which is 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.
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