Cygnus OB2

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• 603 of 1997
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The Milky Way arcs high overhead tonight. This hazy band of stars is divided by dark rifts -- giant clouds of dust that absorb the light from the stars beyond them. This zone of darkness conceals some of the biggest, brightest stars in the galaxy.

An example is a cluster of stars known as Cygnus OB2. It's near the star that connects the body and wings of Cygnus, the swan, which is high overhead in late evening.

The cluster contains about a hundred class "O" stars, and about 2500 class "B" stars -- hence its name. These are the hottest stars of all, shining with the blue-white intensity of an arc welder. They're also some of the heaviest stars -- up to dozens of times the mass of the Sun.

Such stars are not only hot, they're incredibly bright, too -- up to thousands of times brighter than the Sun. From a planet orbiting any of these stars, the nighttime sky would be spectacular. Hundreds of stars would shine so intensely that they'd be almost painful to look at.

The most painful of them all is probably the star cataloged as number 12. Several studies have indicated that it could be the visually brightest star in the entire galaxy. In fact, when you add up all of its energy, it may shine six million times brighter than the Sun.

Star number 12 may end its life with the most powerful type of explosion in the universe. Such a blast would blow most of the star to cosmic dust -- adding new material to the Milky Way's dark rifts.

Script by Damond Benningfield, Copyright 2009

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