Albireo (Beta Cygni) is a beautiful double system in the constellation Cygnus that consists of a bright yellow star (Albireo Aa) and a slightly dimmer blue star companion (Albireo B) which together mark the beak of the celestial swan. The contrast in color between the two stars makes it a popular target for amateur astronomers, but despite Albireo’s “beta” designation, it is only the 5th brightest star in the constellation after Alpha Cygni, Gamma Cygni, Delta Cygni, and Epsilon Cygni.
The constellation of Cygnus is visible from latitudes of between +90 to -40 degrees, and is a regular feature of the northern hemisphere night sky from June to December. Cygnus is also a conspicuous constellation, containing as it does the famous Northern Cross asterism that is made up of the stars Deneb, Sadr (Gamma Cygni) Delta Cygni, and Gienah (Epsilon Cygni). Look for Albireo at the “head” of the Swan, as per the image below where it is position is marked with an arrow.
• Constellation: Cygnus
• Coordinates Albireo Aa: RA 19h 30m 43.286s |Dec. +27° 57′ 34.84″
• Coordinates Albireo B: RA 19h 30m 45.3954s |Dec. +27° 57′ 54.995″
• Distance: (Albireo Aa) 430 light years | (Albireo B) 400 light years
• Star Type: (Albireo Aa) K2II |(Albireo B) B8Ve
• Mass: (Albireo Aa) 14.52 sol | (Albireo B) 3.7 sol
• Radius: (Albireo Aa) 69 sol | (Albireo B) 2.59 sol
• Apparent Magnitude: (Albireo Aa) +3.18 | (Albireo B) +5.09
• Luminosity: (Albireo Aa) 1,200 sol |(Albireo B) 230 sol
• Surface Temperature: (Albireo Aa) 4,270K |(Albireo B) 13,200K
• Rotational Velocity: (Albireo Aa) 1.4 km/sec |(Albireo B) Undetermined
• Age: 100 million years
• Other designations Albireo Aa: ß¹ Cygni, BD+27 3410, HR 7417, HD 183912/183913, HIP 95947, SAO 87301, FK5 732, MCA 55 Aac, NSV 12105
• Other designations Albireo B: ß² Cygni, STF 4043B, BD+27 3411, HD 183914, HIP 95951, HR 7418, SAO 87302
Although the two primary components of the system can be easily split even with modest amateur equipment, it remains uncertain whether ß Cygni A and B are actually orbiting each other, or if they merely form a fortunate optical line-of-sight double star. If the two stars are a true binary system, their angular separation of 35 arcseconds would imply an orbital period of at least 100,000 years. Based on this, and the fact that the two stars have significantly different proper motions, most investigators believe that the two stars merely form an optical double, and that they have no physical relationship to each other.
The two primary stars seem to be surrounded by at least 10 more faint, 10th magnitude suspected companions that are all listed in the Washington Double Star catalogue, with only one being closer to Albireo Aa than Albireo B. The other nine suspected companions are at varying distances from the primary component, with the furthest being 142 seconds of arc away.
The primary component, designated Beta Cygni A (Albireo Aa), is a suspected trinary system, in which the companion stars are designated Albireo Ab and Ac. The latter is located 0.44 seconds of arc away from the primary, giving it an estimated orbital period of 214 years, which is based on the fact that only about 25% of its orbit has been observed.
The other star in the primary pair, designated Albireo B, is a Be-type star with a very high equatorial rotational velocity of at least 250 km/sec, and a spectroscopically-measured effective surface temperature of about 13,200K. Albireo B was also for long a suspected double star, but recent observations have shown this not to be the case.
Albireo’s traditional name appears to be the result of a mistranslation from the ancient Greek word “ornis”, which referred to the entire constellation in which the star appears. It was later translated into Arabic as “urnis”, which was subsequently retranslated in Latin as “Erysimon”, in the mistaken belief that it referred to the Greek name for the plant Sisymbrium officinale. The correct Latin translation, though, should have been “ireo”, but the mistake was nonetheless carried over into the Arabo-Latin Almagest of 1515. In time, the confusion that stemmed from the original mistranslation was compounded when “ab ireo” was thought to be a mistranslation or miscopy of an Arabic term or word by an unknown scribe, and “ab ireo” was subsequently changed into “al-bireo”. However, medieval Arab records list Albireo as “minqar al-dajajah”, which translates into Latin as “Rostrum Gallina” meaning “the hen’s beak”.