Cygnus

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The swan flies high overhead on summer nights, its body and wings immersed in the subtle glow of the Milky Way. And it's easy to pick out because the pattern formed by its brightest stars really does look like a graceful bird -- and because the star at its tail is one of the brightest in the night sky.

Cygnus is high in the east at nightfall and soars directly overhead later on.

Three bright stars outline the swan's body. From nose to tail, they're Albireo, Sadr, and Deneb.

Albireo is actually a double star -- one of the most popular among regular skywatchers. Through a telescope, one of the stars looks blue, while the other is golden. The two stars are so far apart that they may or may not be gravitationally bound to each other. They may just happen to line up in the same direction in the sky.

Sadr forms the intersection of the body and wings. It's a supergiant -- a star that's far larger and more massive than the Sun, and tens of thousands of times brighter. Dense clouds of gas and dust absorb some of the star's light, cutting its brightness in our sky by about half.

Deneb is a supergiant, too. In fact, it may be a near-twin to Sadr. It's a little brighter and thousands of degrees hotter. Most important, it's probably a little more massive. The difference means that while Sadr's fate is a little uncertain, Deneb's is probably set: It will blast itself to bits as a supernova.

We'll have more about Deneb tomorrow.

Script by Damond Benningfield, Copyright 2009

For more skywatching tips, astronomy news, and much more, read StarDate magazine.