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BOB HIRSHON (host):
How far is that star?…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? For the first part of the answer, we consulted Raja Guhathakurta, a professor of astronomy and astrophysics at the University of California at Santa Cruz. For stars up to a few hundred light years away, he says you can use a geometric method called parallax.
RAJA GUHATHAKURTA (UC Santa Cruz): As the earth goes around the sun, our viewing perspective for distance to us changes, naturally.
HIRSHON: So what happens is that stars that are closer to us will appear to change position relative to stars that are farther away. By comparing a star’s position now to what it is six months later, you can calculate its distance. Guhathakurta says thousands of stars can be measured this way. But for even more distant stars, astronomers need to use other techniques. If you’ve got a science question, call us at 1-800-WHY-ISIT. I’m Bob Hirshon for AAAS, the science society.