Keeping accurate time and determining age are two crucial, constant goals in science. In the 1700s the proof and construction of an elegant, precise maritime clock opened up much safer and more efficient ocean exploration and provided a way forward for more accurate mapping on Earth. Before then, mariners and astronomers alike were both, literally, at sea.

Likewise, until now, determining the age of stars has been equivalent only to saying that a person is young or old, and our guesses of someones age are typically off by as much as 15 percent. But by building on the work of others (as it goes in science) and carefully working out for over a decade how to construct a clock to measure the ages of stars, Sydney Barnes, of the Leibniz-Institut fuer Astophysik Potsdam (AIP), Germany, derived an elegant and extraordinary method he named gyrochronology to derive a stars age from its spin rate and its mass.

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Barnes named his method from the Greek gyros which equals rotation, chronos which means time and logos for study.

We here develop an improved way of using a rotating star as a clock, set it using the sun and demonstrate that it keeps time well, wrote Barnes in 2007 (PDF), but his work on this groundbreaking theory goes back to 2000.

Now, in a new study published in the journal Nature and announced today at the 225th American Astronomical Society meeting in Seattle, Barnes and his colleagues have measured more than 20 sun-like stars believed to have identical ages, all belonging to a single a star cluster, and by showing that gyrochronology gives an age of 2.5 billion years for all of them to within 10 percent, have essentially proven the method beyond reasonable doubt.

In fact, the uncertainty on the gyro-age of the cluster as a whole is two percent, which means that the new clock is now more precise than the ones used to set it, said Barnes.

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The studys team, led by Soren Meibom, of the Harvard-Smithsonian Center for Astrophysics, in Cambridge, Mass., used NASAs Kepler Space Telescope to measure the tiny variations of starlight over days or weeks that are caused as dark spots on the surfaces of the stars are alternately revealed and hidden by the rotation.

These space telescope measurements represent the culmination of a hard slog for over a decade by Meibom, Barnes and the other co-authors using ground-based telescopes to acquire and analyze the required support observations, to develop the theoretical framework adequately and to measure and interpret other appropriate clusters for possible deviations.

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