Mare Nubium contains a diverse range of interesting features. The most notable is Rupes Recta, a mid mare fault also known as Straight Wall. It extends north-south for 100 km. The west-facing slope is up to 2.5 km across, but is not steep as the height only ranges up to 0.3 km. At several points along its length you can see disturbances due to ancient land slides. There are only a handful of similar isolated faults. The small but deep (3.47 km) crater to the west side of the fault is Birt (17 km) and its small companion Birt A (6.8 km). Birt Rille, formally called Rima Birt, is a volcanic channel 1.5 km wide and 50 km in length. The rille arose from a caldera (Birt E, 5 km) at the northern end which sits atop a low dome that is only evident at low angles of lighting. The rille terminates at Birt F (3 km).
Waning Moon, 45% full