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.
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.