After you have worn yourself out on Eratosthenes and Copernicus and see all the features around Plato, 8-9 days after new moon, you may notice a beautifully terraced crater in the south just west of Arzachel and Rupes Recta. This is Bullialdus (63km dia.) with a floor 3.5km below the rim and a multi-peaked “central peak” rising over a kilometer above that crater floor. This formation is only 1.1-3.2 billion years old making it of Eratosthean age, before Copernican but after Imbrian ages. Its isolation on the surrounding plain of southern Mare Nubium makes it stand out. There is a good hatch work of ejecta outside the crater walls extending out about a crater radius. South of this crater is Bullialdus A (26km) a shallow crater undoubtedly filled with ejecta from the Bullialdus impact, and a bit farther south is slightly smaller Bullialdus B (21km) and then west (left) of that is a rather polygonal but similarly sized crater, Konig (23km). Apollo 16 got a splendid view of these group and it’s worth looking up on the web.
There are a number of ghost and partial craters in this frame surrounding Bullialdus. The most obvious can be seen at the top and bottom of the image, Lubiniezky (40km) and Kies (46km) respectively. Due west of Bullialdus you can see two more ruined. nearly ghost, craters, The closest one is Agatharchides P (65km) with the little cirque cut out in the lower left which is Agatharchides N (21km) and a little further west is Agatharchides itself (51km). South of these craters is another ghost crater crossed by rimae, or stretch marks from Mare Humorum farther to the west. When that mare cooled there was a subsidence as the rock contracted leaving the parallel arc graben like rimae you see here. The crater in question is Hippalus (57km) listed by the Virtual Moon Atlas as an “Exceptional formation” but as shown here, not at all unique in Mare Nubium.
On the opposite side of Bullialdus, to the right or east is an unusual ghost crater, Gould (32km) that is mostly just the west wall of the crater. South of this is a heart-shaped crater, Wolf. It is listed as 25km diameter but it is anything but circular. This formation, which includes the irregular walls and flooding, probably consists of at least 3 separate impacts. The thing I find fascinating about this feature is how it changes with changing illumination during the lunar day, but that’s another article in itself! Don’t hesitate to explore this area when it is available. Your efforts will be well rewarded.
