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May 27, 2010

European astronomer Friedrich von Struve observed and catalogued thousands of binary stars -- pairs of stars that are gravitationally bound to each other. But a system that he first observed in 1829 was so striking that he gave it a special name: Pulcherrima -- "the most beautiful." The name honors the contrasting colors of the two stars: one looks orange, while the other looks blue-white or even green.

The star is better known by an even older name, Izar, meaning "girdle," because it represents the middle of Bootes, the herdsman.

Regardless of what you call it, though, most skywatchers agree with Struve's assessment: Seen through a telescope, the pair is quite a beauty.

The orange star is a giant. It's burned through its original hydrogen fuel and is nearing the end of its life, so it's puffed up to many times the Sun's diameter.

Its companion is technically a white star -- it looks bluish only when it's compared to the orange giant. It's less massive than the orange star, so it has a lot longer to go before it reaches its own "giant" phase. It shines white because its surface is thousands of degrees hotter than its companion's is.

Boötes is in the east at nightfall. Its brightest star is brilliant yellow-orange Arcturus. Izar is to the left of Arcturus. To the unaided eye, it looks like a single point of light. But a telescope reveals the true beauty of this colorful duo.

We'll have more about Boötes tomorrow.

Script by Damond Benningfield, Copyright 2010

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