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D. How Astronomers Detect Extrasolar Planets

Narrator: This is Science Today. Our sun contains nine planets and scientists have long wondered whether or not other stars in the night sky might also harbor planets similar to our own. Geoff Marcy, a professor of astronomy at the University of California, Berkeley, says there's been an ongoing search for many years now to find extrasolar planets.

Marcy: You can't actually see directly the planet orbiting another star - the glare from the star is just too bright to see the little tiny dot of light that would be the planet. So instead, what we do is we watch the stars to see if they move in space - wobble around and around.

Narrator: That would indicate a gravitational tug from the orbiting planet. But Marcy recently witnessed one of these planets cross in front of its star, causing it to dim.

Marcy: We've always known that there was a chance that if you're lucky, the orbital plane of the motion of the planet would take the planet right in front of the star - just by luck. And so the transit of the planet actually happened just as we had imaged and always hoped.

Narrator: For Science Today, I'm Larissa Branin.