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For most birds, it’s the beautiful feathers that get most of the attention. And that’s pretty much the case for Cygnus, the celestial swan. To the eye alone, its most impressive sight is Deneb, the bright star that represents its tail feathers.
If you look more closely, though, the swan’s fainter beak is far more colorful. Through a telescope, that single pinpoint of light becomes double — one of them golden orange, the other a dazzling blue-white. That contrast makes Albireo one of the favorite double-star targets in the sky.
The golden star is actually two stars on its own. They’re so close together that they blur into a single point of light even through a telescope. One of them is orange, while the other is white.
The other visible member of Albireo is thousands of degrees hotter than the Sun, hence the blue-white color.
It’s not clear if the two visible components are a true binary or just happen to line up in the same direction in the sky. Astronomers determine if two stars are a binary by measuring their relative motions across the sky. If they are bound to each other, then their paths curve around each other. But the components of Albireo are so far apart that there hasn’t been enough time to see that.
Albireo is on good display on summer nights. Cygnus is high in the east at nightfall, with its body parallel to the horizon. Brilliant Deneb is at the left end of the body, with Albireo at the right.
More about Cygnus tomorrow.
Script by Damond Benningfield, Copyright 2012