StarDate: December 15, 2009

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A bevy of brilliant stars congregates in the east this evening, and every star has a story to tell. Sirius, the brightest star in the night sky, has a "dead" companion. Blue-white Rigel, the brightest star of Orion, is many thousands of degrees hotter than the Sun, while orange Betelgeuse, on the constellation's opposite side, is thousands of degrees cooler. And Castor, one of the "twins" of Gemini, is actually a family of six stars.

Astronomers have learned these stories and many more through a technique called spectroscopy. The technique splits the light from an astronomical object into its individual wavelengths -- like a rainbow of colors. Where the wavelengths are strongest tells us how hot an object is -- hotter objects look bluer, while cooler ones are redder.

Individual chemical elements leave their "fingerprints" in the rainbow -- patterns of bright or dark lines at specific wavelengths. From these patterns, astronomers can tell what elements a star contains.

And an object's motion through space causes a shift in these patterns. If an object is moving away from us, they're shifted to redder wavelengths; if it's moving toward us, they're shifted to bluer wavelengths. The size of the shift reveals how fast the object is moving.

And if the lines appear to "wiggle" a bit, it means the object has companions. This technique has revealed hundreds of planets in other star systems -- some of the many stories told by starlight.

Script by Damond Benningfield, Copyright 2009

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