Burnham's is indeed out of date., at least in this instance. I believe that Albireo's true binary nature was only confirmed in the past 20 years or so. As Joe posted in reply, the yellow primary is a spectroscopic binary, although I didn't know that before. I believe that the information that Joe provided is a bit misleading: Albireo is about 380 light years distant from Earth - that isn't the distance between the two components. Joe, did you find the separation given anywhere (in other than angular distance)? Kim

-----Original Message----- From: utah-astronomy-bounces@mailman.xmission.com [mailto:utah-astronomy- bounces@mailman.xmission.com] On Behalf Of M Wilson Sent: Sunday, May 17, 2009 12:15 AM To: Utah astronomy blog Subject: [Utah-astronomy] Albireo: a double star?

I found this a few years ago in the 1978 edition of Burnham's (Burnbaum's) Celestial Handbook Vol. II, page 754, third paragraph:

"Albireo is believed to be a physical pair, although no evidence of ortibal motion has been detected since the first observations of F.G.W. Struve in 1832."

Most of us, including myself, have been telling the public for years that the two were gravitationally bound.  Looks like the proof is lacking or is Burnham's is out-of-date?

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