Albireo Ac is the hot close companion of Albireo’s orange giant, too near its partner for the eye or a small telescope to separate from it.
At a glance
| type | blue-white star (class B) |
|---|---|
| distance from the Sun | 434 light-years (133 pc) |
| its light left it | 434 years ago |
| luminosity | 40 × the Sun |
| radius | 2.1 × the Sun |
| surface temperature | 10,000 K |
Read off the piece’s own catalogue, the same values it draws with.
About Albireo Ac
Through a telescope Albireo shows two stars: a golden one and a blue one. The golden star, Albireo A, is not single. Interferometry, which combines light to reach far finer detail than an ordinary image, revealed a hot blue-white companion, Ac, in orbit very close to the orange giant.
The two form a genuine binary, and their orbit has been followed long enough to chart it. The giant dominates the light, so in the colour of the golden star you are seeing mostly the cool giant, with Ac adding only a little blue.
Albireo marks the head of the swan in Cygnus, at the foot of the figure called the Northern Cross.
What you see in the piece
Fly to Albireo and Ac separates from the orange giant as a small blue-white point; from Earth the two merge into the single golden star of the famous pair.
Questions
Is Albireo a triple star?
The golden star of Albireo is itself a close binary, an orange giant with the blue-white companion Ac. Whether the blue star Albireo B is bound to them is still debated.
How far away is Albireo Ac?
It is 434 light-years (133 pc) from the Sun.