Awesome Albireo, Summer’s Most Spectacular Double Star

Albireo in the Northern Cross is summer’s #1 double star treat. Don’t miss the opportunity to use your small telescope for a look. Star colors have to do with temperature: the blue star is 20,000 F  (11,100 C), considerably hotter than the 8,000 F (4,400 C) orange star. Credit: John Chumack

Summer’s most colorful double star is calling your name.  Albireo (al-BEER-ee-oh), in the foot of the Northern Cross, is a gorgeous gold and pale blue pair that even the smallest telescope can split. With good focus and steady hands, 10x binoculars will cleave it.

The two stars, which appear to the naked eye as a single star, are about 380 light years away and so far apart from each other, that to be honest, astronomers still aren’t certain they’re physically connected. Assuming they’re gravitationally bound, they orbit one another with a period upward of 75,000 years. Albireo became a triple star in 1976, when astronomers discovered that the brighter orange star had a very close companion beyond the reach of amateur telescopes.

Look high in the southeastern sky at nightfall in late July and early August to find the three bright stars that mark the corners of the Summer Triangle. Albireo shines at 3rd magnitude (one level fainter than the Big Dipper stars) and is located about one outstretched fist below Deneb in the Northern Cross. Created with Stellarium

Luckily for skywatchers, Albireo is easy find. Using the little map, look high up in the southeast at nightfall to trace the grand outline of the Summer Triangle defined by the bright stars Vega, Deneb and Altair.

Deneb in the Northern Cross (also known as Cygnus the Swan) sits at the top of the Triangle and marks the “head” of the Northern Cross (known formally as Cygnus the Swan); Albireo lies at the “foot” of the cross. Albireo is well placed June through early autumn as it swings across the southern sky.

I like to use my lowest magnification when I stop by for a look in the telescope. Not only are the colors more apparent but the two stars shine crisply against the diamond dust of fainter Milky Way stars.

Albireo marks the foot of the Cross but more traditionally the head of Cygnus the Swan. Credit: Bode’s star atlas

The origin of the name Albireo is rooted in the Arabic language but became corrupted through mistranslation and misunderstandings to the point that it no longer means anything in particular. No matter. It still sounds very good to the ear, and looks even better to the eye.

Albireo has lots of company. Somewhere around half of all stars are double or multiple. All manner of pairs exist – everything from almost impossible to split to widely-separated duos you can sever with your naked eye. They’re everywhere. I’ll often stumble across a potential double, note its position and backcheck to see if it’s a real, physical pair or one of many line-of-sight or “optical” doubles that masquerade as the real thing.

Dust off that telescope and make Albireo your next stop on a summer night.

9 Responses

  1. caralex

    Bob, has no astronomer, since the start of the telescopic age, seen any proper motion between the two components, that would indicate whether they’re a true binary, or a line of sight effect?

    1. astrobob

      To my knowledge, no. The two share a common proper motion through space however and the Hipparcos satellite places the two at about the same distance making it likely they’re a real double. However it’s also possible they’re moving parallel through space – perhaps they were once part of a cluster.

    1. astrobob

      Hi Anthony,
      If you’re referring to the star Albireo in the foot of Cygnus (Northern Cross), it’s been the same brightness for centuries. Could you be referring to something else?

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