Albireo
What is Albireo?
Stars· Distance ~430 ly · the sky's loveliest double. The star at the beak of Cygnus, the Swan. A small telescope shows a golden star and a blue star side by side, making it a famous and beautiful double. Whether the two are truly a pair is still unsettled.
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Distance and spectral type
Albireo is about 434 light-years away, a orange bright giant (spectral type K3II+...), in the constellation Cygnus. Its apparent magnitude is 3.1, visible to the naked eye.
Stellar figures
| Distance | ~365 & ~395 ly (A, B — Gaia) |
|---|---|
| Magnitude | 3.1 (combined) |
| Colours | golden giant + blue companion |
| Constellation | Cygnus |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Albireo, a name born from a Latin misunderstanding
The name Albireo sounds Arabic, but it actually grew out of a misunderstanding. In Ptolemy's star catalogue from the second century, this star was described as the one on the bird's beak. The catalogue was translated into Arabic, and in the Middle Ages it was translated again into Latin. Along the way, a Latin phrase with no clear meaning, 'ab ireo', found its way into the text.
Later readers took the phrase for an Arabic star name. A letter 'l' seems to have been added by mistake, as if it began with the Arabic 'al', and so it became 'Albireo'. The accidental name stayed in use for centuries, and in 2016 the International Astronomical Union made Albireo the star's official name. A small slip, made while the text passed from language to language, lives on as the name of a star.
The star in depth
Albireo marks the head of Cygnus, at the tip of the Swan's beak. To the naked eye it is an ordinary third-magnitude star, about 365 and 395 light-years away (the two stars, measured by Gaia). Through a telescope, though, it changes completely: a golden-orange star and a crisp blue star shine side by side, 35 arcseconds apart. The contrast is so striking that it is always popular at stargazing events.
The two stars differ in colour because their surfaces differ in temperature. Cooler stars glow redder and hotter stars bluer. The bright one, Albireo A, is a giant that has used up much of its fuel and swollen, with a surface of about 4,400 K that gives it an orange glow. Blue Albireo B is a hot star with a surface of about 13,000 K. That is why Albireo is often used to show how a star's colour reveals its temperature.
Whether the two stars orbit each other or merely line up by chance has long been debated. The Gaia satellite has measured their distances and motions precisely, but the data are not yet enough to decide either way. On summer nights, start from Deneb inside the Summer Triangle and follow the Swan's neck down to its beak to find Albireo. Select Albireo in the Sky view to see the Swan's long body.
Frequently asked
- How far is Albireo from Earth?
- The distance of Albireo is ~365 & ~395 ly (A, B — Gaia).
- How bright is Albireo (apparent magnitude)?
- The magnitude of Albireo is 3.1 (combined).
- Which constellation is Albireo in?
- Albireo lies in the constellation Cygnus.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.