Using the unique capabilities of NASA's Kepler space telescope, Soren Meibom (CfA) and his collaborators measured the rotation rates for stars in a 1-billion-year-old cluster called NGC 6811. They found rotation periods ranging from 1 to 11 days (with hotter, more massive stars spinning faster), compared to the 30-day spin rate of our Sun. More importantly, they found a strong relationship between stellar mass and rotation rate, with little scatter. This result confirms that gyrochronology is a promising new method to learn the ages of isolated stars. Credit: Anthony Ayiomamitis