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Deepsky Top-100 (16): Beautiful Albireo
In my list of favourite deepsky objects for suburban backyards you will find only a few galaxies. Because of the severe light pollution these delicate structures with low surface brightness visually loose almost all detail or, even worse, aren't visible at all through my 8-inch telescope. I compensate this by adding some beautiful stars, double stars and multiple stars to my Deepsky Top-100.

My all time favourite double star is Beta Cygni, better known as Albireo. I have been observing Albireo for more than
25 years using a wide variety of telescopes and binoculars. For me personally this wonderful double hasn't lost much of its charm. I find Albireo at its best through my 4-inch refractor at a low magnification (30x): a superb golden-blue pair of stars against a more or less black background, a true celestial gem.
The name Albireo, seems to be the result of a mis-translation of the term Ab Ireo from the 1515 edition of Ptolemy's Almagest (star catalogue). According to R.H. Allen (Star Names, their lore and meaning) the original Arabian name of Albireo was Al Minar al Dajajah, the hen's beak. Deneb, marking the tail of the Swan, comes from Al Dhanab al Dajajah, the hen's tail. Gamma Cygni or Sadr, right at the heart of the Swan comes from Al Sadr al Dajajah, meaning the hen's breast.

Albireo is very easy to locate (see map below). First look for the constellation Cygnus, the Swan. In light-polluted suburban areas you will be able to identify the Swan as a large cross in the sky, with the bright white Deneb (Alpha Cygni) at the tail of the Swan and Albireo (Beta Cygni) at the swan's head.

Albireo consists of 2 components, a bright magnitude 3.1 orange class K giant star (like Arcturus) which is fusing helium into carbon and a magnitude 5.1 blue-white class B-dwarf that transforms hydrogen into helium (like our own Sun). The brighter A component has a luminosity of more than 700 Suns, while the dimmer B component is a 100 times the (visual) solar luminosity. The stars are separated by 34". The position angle of the B component is 54°. Albireo is probably a true physical double star, although hard evidence of orbital motion has not yet been detected. Recent measurements place them at a distance of almost 400 light years. According to these same measurements, the distance between the two stars is about 9 light years. However, the uncertainty of the distance of each of the components is about 25 light years.

So go out and observe Albireo! For me personally, nothing beats the "live" view of a beautiful double star. There is no sketch or image that comes even near to what you see through the eyepiece.

Clear Skies!

image
Click to enlarge (Image from Skytools 2 by CapellaSoft)
Posted by Math on 07/27 at 01:17 PM
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