Pitatus (Figure 10.15) is a large crater with a flooded floor on the southern edge of the Mare Nubium. The walls have been badly eroded in places, especially to the north, and it is joined by Hesiodus on its western rim. Pitatus is 100 kilometers in diameter and has a relatively small central mountain peak noticeably offset to the
west of the crater. Although Pitatus' floor is flooded, there are some delicate rilles there, but these are very subtle features and not comparable to the spectacular rille networks found, for example, in Posidonius and Gassendi. Two hundred kilometers northeast of Pitatus' outer wall you will find the crater Birt and the feature known as Rupes Recta, or the Straight Wall (Figure 10.16), or Straight Fault. Whenever I think of this feature, I recall numerous talks I attended by Patrick Moore when he would say "It's called the Straight Wall because it's not straight and it's not a wall." This always got a good laugh from the audience! Patrick was right, but it is one of the most noticeable linear features on the Moon, even if it does have a slight curve to it. It is a geological fault that has a slope of about seven degrees, but this is enough to make it look like a wall under a low Sun angle. Although relatively small, at 17 kilometers in diameter, the crater Birt is a crater worthy of a few moments study, too. It is an almost perfect small circle, apart from where it joins the smaller crater Birt A and Rima Birt, a 50-kilometer-long rille lies to its northwest, joining the tiny craters Birt F and Birt E.
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