Albireo - The Swan's Beak

by Jeff Brydges

High overhead during late summer spans the distant soft glow of millions of stars in our Milky Way Galaxy. Embedded in this Great Cygnus starcloud lies the most attractive double star in the entire heavens. Albireo (Beta Cygni) is a rather discrete 3rd magnitude star lying near the center of the asterism called the "Summer Triangle". Albireo, pronounced (al-BURR-ee-oh) represents the Swan's Beak. It is the finest double star available to amateur astronomers with small telescopes. Why is this so? Because Albireo is fairly bright and easy to locate, shows off a beautiful color contrast, and needs little optical power to be appreciated.

Albireo was first noted in the mid-1700's. Later in the 1700's Christian Mayer observed this pairing on 102 occasions. Albireo consists of a magnitude 3.1 bright yellow giant star, and a 5.1 magnitude companion. Together they span some 34.5" of sky. The companion can be found northeast of the primary at a P.A. of 54 degrees. Some older astronomical sources point to this duo as being an optical pairing rather than a true physical binary system. More recent datum collected by the HIPPARCOS satellite verifies Albireo is an actual binary system. At a distance of 385 light years the projected separation is some 400 billion miles. Fifty of our Solar Systems would fill the gap if stacked end to end. This binary system must take about 100,000 years to complete an orbit.

The yellow giant primary is also a very close binary system with a 5.5 magnitude companion star about 0.4" away at a P.A. of 142 degrees (1995). It was first detected by H.A. McAlister on June 6, 1977 using a speckle interferometer with the 158" reflector on Kitt Peak. It was later spied by C.E. Worley using the 26" reflector at the U.S. Naval Observatory in 1979. Since its discovery it has decreased in separation 0.04" and 50 degrees in P.A. The companion known as Beta Cygni A is a main sequence star with a spectrum of B0V.

Beta Cygni A has a luminosity of 1000 suns, and a spectrum of K3II. Its diameter is about 80 times greater than our Sun. The companion Cygni B is a blue main sequence star with a spectrum of B9.5V. It has a diameter of about 1.5 times the Sun, and a luminosity of 95 suns. The blue companion has a temperature three times greater than its cooler giant neighbor so that this pair displays an excellent color contrast.

In my 3" telescope at 21x, with a 2 degree field of view, I see Albireo's components nearly in contact, with colors of topaz and sapphire appearing to be suspended in 3D against the numerous background stars of the Milky Way. What a magnificent sight!

To enjoy this grand double star, start at Deneb (Alpha Cygni) and move southwestward down the length of the "Northern Cross" some 25 degrees until you find a 3rd magnitude star at its base. Or use these coordinates: R.A. 19h 30m 43.1s, Dec. +27d 57m 35s. Put in a low power eyepiece and savor this wonder of our Universe.