LONG BEACH, CALIF.—One of the unnerving aspects of astronomy as a science is how astronomers continue to argue over measurements you’d have thought they settled long ago. A good recent example is the mass of our own Milky Way galaxy. Estimates keep swinging back and forth, and our galaxy and the Andromeda galaxy periodically switch places as the alpha galaxy of the local cosmos. A new study announced at the American Astronomical Society’s conference suggests that astronomers may finally be starting to converge on a consensus—and, in a counterexample to the usual trend of relegating humanity to the cosmic backwaters, our Milky Way looks like the bigger one after all. (My colleague Steve Mirsky also describes the study on today’s podcast.)

To weigh the Milky Way, Mark Reid of the Harvard-Smithsonian Center for Astrophysics and his colleagues tracked the motion of bright gaseous clouds in 12 star-forming regions scattered over the galaxy. They observed the clouds with the Very Long Baseline Array, a network of radio telescopes stretching from Hawaii to St. Croix which work in unison as a single planet-sized telescope. The network is so sharp-eyed that it can see clouds on the other side of the galaxy inching across the sky. The team combined these observations with measurements of the Doppler effect to deduce the clouds’ full three-dimensional orbital velocity: 254 +/– 16 kilometers per second.

some unseen dark matter.

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