The average distance to the moon is about 1.28 light seconds. Today the Dawn probe is about 1.5 light seconds from Ceres. http://dawn.jpl.nasa.gov/mission/live_shots.asp Ceres diameter is about 1000 km, which means roughly 1/3 the size of the moon (diam = 3500 km) The Dawn spacecraft is beginning to get into the range of proximity where Ceres will begin to appear roughly comparable in size to how the moon looks from Earth. Not yet---at the moment it would look only a QUARTER as big, one fourth the angular size of the moon seen from Earth. But getting there.