At (Cosmic) Arm’s Length

From Science:Sun

Astronomers have resolved a long-standing debate about how far our sun is from a nearby cluster of stars in the Milky Way. The new measurement may help scientists more accurately map out the shape of the galaxy, as well as determine the amount of gravitational “muscle” its star-filled arms contain.

The Milky Way is composed of several spiral arms–long, thin bands of bright, young stars that fan out from the center like the blades of a pinwheel. Our sun is located in the rather short Orion spiral arm, which is tucked inside the larger Perseus spiral arm. But astronomers aren’t sure how far away the Perseus arm is, and knowing that could help them determine the true size and makeup of the Milky Way. Two separate measurements of Perseus’ distance have given values that differ by a factor of 2–a large discrepancy even by astronomy standards, says Mark Reid of the Harvard-Smithsonian Center for Astrophysics.

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