The center supports an active program of observational astronomy. Current activity focuses on optical studies of stellar explosions, multi wavelength studies of the transient sky, gravitational lensing, and the study of the solar system's comets. Center observers are major partners in the leading international PTF collaboration for optical monitoring of the transient sky, and enjoy access to leading observatories. Students and post-docs spend time at Caltech and use the Keck & Palomar observatories through a student exchange program.