A lunar transit of the sun captured during calibration of STEREO B's ultraviolet imaging cameras. A transit is the astronomical event that occurs when one celestial body appears to move across the face of another celestial body, as seen by an observer at some particular vantage point. In this video the Moon appears smaller than it does from Earth because the satellite's viewpoint is farther from the Moon than the Earth is.Film credit: STEREO mission (NASA)