When the libration is right you get a rare view of a huge crater that is normally out of sight. Here you can see it as a large oval near the limb with black basaltic flooded areas on its floor and a sparkling white offset central peak. This is the great crater Humbolt (213km dia.) named after the explorer, naturalist and geographer that was the mentor of Louis Agassiz. This presentation gives us a nice demonstration of just how shallow these grand depressions are. It has huge cliffs on the far side and a floor covered with rimae just barely seen from earth view here. These were likely caused from settling of the flooded floor as it cooled. Adjacent to the near side of Humbolt is the ghostly outline the crater Phillips (128km). Just beyond Phillips is a small bright floored crater Phillips A (13km).
In the upper left corner of this image is the fabulous crater Petavius with the famous large rima running out to the lower left from the bright splatter of the central peaks. Then directly between Petavius and Humbolt is the outline of the crater Legendre (82km).