This illustration shows the Transiting Exoplanet Survey Satellite, or TESS, gazing at a star with several planets. Designed to detect the telltale dips in a star's brightness caused by a planet passing in front of the star, TESS also excels at studying how stars vary in brightness for other reasons, such as stellar activity. Researchers recently used observations from TESS to amass a catalog of stellar rotation periods for more than a million stars. This catalog will help researchers understand how stars evolve and even allow them to study the structure of the Milky Way. To learn more about this work, you can read our AAS Nova highlight and the corresponding research article in the Astrophysical Journal Supplements. [NASA's Goddard Space Flight Center]