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BOB HIRSHON (host):
To infinity and beyond…I’m Bob Hirshon and this is Science Update.
Listener Jack Downs of Chicago, Illinois, asked: How do you know how far away a star is? We consulted Raja Guhathakurta, a professor of astronomy and astrophysics at the University of California at Santa Cruz. He says astronomers have calculated distances to thousands of stars using a geometric method called parallax. But that only works for stars up to a few hundred light years away. For stars farther than that, he says astronomers compare their brightness and color spectrum to the stars they know.
RAJA GUHATHAKURTA (UC Santa Cruz): Every time you find a star that’s a twin of one of these stars, then you can infer the wattage of that distant star. And once you know its wattage and you know how bright it appears to be, you can figure out its distance.
HIRSHON: If you’ve got a science question, call us at 1-800-WHY-ISIT. I’m Bob Hirshon for AAAS, the science society.