Three hundred kilometers southeast of Gassendi you will find a truly magnificent gem on the Moon: a region that looks like a giant cat had frantically scratched the lunar surface with its claws (to the lower right of Figure 10.17). This is the region east of the ruined and flooded crater Hippalus and its associated rilles. The rilles are northwest of the striking crater pair Mercator and Campanus. There is so much to describe about this complex region that one could almost write a chapter on it alone. Fortunately, a picture speaks a thousand words and so I am spared from trying to describe the scene. The whole area straddles the boundary between the Mare Nubium and the Mare Humorum and though the Hippalus rilles are the most eye-catching feature there is plenty more to interest the visual observer or the webcam imager. The 50-kilometer craters Mercator and Campanus appear, under average seeing, to have fairly smooth, flooded floors (except for the rubble and the big craterlet on the floor of Campanus). Mercator's floor in particular looks pretty smooth and featureless. But catch a few dozen good webcam frames on a night of excellent seeing and even this crater's floor reveals tiny craterlets. Nearby the flooded crater Kies will catch your eye and further north the magnificent 60-kilometer Bullialdus is another favorite with a textbook central peak and terraced walls.
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