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BOB HIRSHON (host):
Mapping the Milky Way. I’m Bob Hirshon and this is Science Update.
Astronomers have made an important advance in mapping our galaxy—the Milky Way. It has a spiral form, with arms that swirl around the center like a pinwheel. But Harvard-Smithsonian astronomer Mark Reid says the distance to the nearest arm, called the Perseus Arm, has been difficult to pin down.
MARK REID (Harvard-Smithsonian):
And so what we’ve done is use the simplest, most accurate technique in astronomy and it’s the same technique a surveyor uses on the ground, often called triangulation.
HIRSHON:
Triangulation gauges distance by measuring how something shifts against the background when viewed from two different places. The astronomers discovered the Perseus arm is 6,360 light-years away by looking at it with powerful telescopes from opposite points in the Earth’s orbit around the sun.
I’m Bob Hirshon, for AAAS, the science society.