Thanks to James B. Kaler. These contents are the property of the author and are reproduced from original without the author's express consent because of fair use and valid educational purposes.


One of the great small-telescope showpieces of the sky, Albireo, the third-magnitude Beta star of Cygnus, is a magnificent double whose components have contrasting blue and golden colors. Star colors are usually subtle, ranging from a warm orange red to a hint of blue on white depending on the viewer's eyes. But put a star of one color next to one of another, and the eye seems to exaggerate both, delighting the follower of double-star astronomy. Waxing romantic, astronomers have called the pair topaz and sapphire. With a separation of 34 seconds of arc, the pair is easily seen at low telescopic power. The name has a magnificently confused and mistranslated origin in which it means nothing at all with regard to its position at the head of Cygnus the Swan. Albireo beautifully shows how an apparently single star as viewed through the telescope can actually be double, such "binary" stars appearing all over the sky. Somewhere around half, or even more, of the local stars are actually members of some kind of double or multiple system, the stars in orbit about each other. The stars that make Albireo, about 380 light years away, are quite far apart however, and if actually attached graviationally have an extremely long orbit with a period estimated to be about 7300 years. The brighter yellow-colored member of Albireo is a much closer double, the two stars not separable in the telescope. It consists of a bright, but cool, evolving giant coupled with a dimmer but hotter "dwarf," a star that, like the Sun, fuses hydrogen into helium in its core. The dimmer fifth magnitude blue component of Albiero is, so far as we know, single, and is a blue dwarf just a bit cooler than the companion to the yellow star. It is a very interesting star in its own right, as it is a rapid rotator that is losing matter and is surrounded by a disk of gas of its own making.