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Stellar Ages from Stellar Rotation

Our ability to determine stellar ages from measurements of stellar rotation, hinges on how well we can measure the dependence of rotation on age for stars of different masses. Rotation periods for stars in open clusters are essential to determine the relations between stellar age, rotation, and mass (color). Until recently, ambiguities in vsini data and lack of cluster membership information, prevented a clear empirical definition of the dependence of rotation on color. Direct measurements of stellar rotation periods for members in young clusters have now revealed a well-defined period-color relation. We show new results for the open clusters M35 and M34. However, rotation periods based on ground-based observations are limited to young clusters. The Hyades represent the oldest coeval population of stars with measured rotation periods. Measurements of rotation periods for older stars are needed to properly constrain the dependence of stellar rotation on age. We present our plans to use the Kepler space telescope to measure rotation periods in clusters as old as and older than the Sun.