Moonwatch
Piccolomini is an 88km crater situated to the south of Mare Nectaris. It also lies at the southern end of the distinctive Rupes Altai, a 480km, curved cliff structure, concentric with the edge of Mare Nectaris. The impact that formed Piccolomini occurred after the formation of Rupes Altai.
Piccolomini is embedded within a bright highland landscape and this makes the crater somewhat tricky to see under high illumination. During periods when the terminator is nearby, the crater shows a wealth of detail. Piccolomini is around 4.2km deep measured rim to floor, with a couple of peaks on the western section of the rim reaching heights of around 4.5km. The rim looks fairly continuous except when the Sun angle is low. At such times,
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the southeast section appears less distinct, almost smoothed over. One theory suggests that this is because the material here has collapsed into the centre of the crater, forming a smoother landscape leading down to Piccolomini’s floor.
Most of the inner rim is heavily terraced, leading down to what appears to be a relatively smooth floor surface. The terraces encroach furthest toward the centre of the crater in the southern half, possibly something to do with the section of Rupes Altai which would have been here when Piccolomini’s impact hit. At the centre of the crater is a magnificent central mountain complex rising to a height of around 2.5km. There is a small 3.5km craterlet located to the north of the central mountains, a good test for an 8-inch or larger telescope.
The area immediately north of Piccolomini appears as a pentagonal pattern of smaller craters, hexagonal if you include the smaller 12km craterlet to the north, Piccolomini B. Most distinctive is 23km Piccolomini M which appears to touch the northern edge of its primary crater. Northeast is 17km Piccolomini D, then 18km E. B lies to the west-northwest of E, with overlapping 16km A and 11km O to the south-southwest of B. Looking far less distinct is 26km C between O and M, a much more eroded crater in comparison to the others. In the centre of the pentagon is 8km X, another eroded craterlet which can be hard to see when the sun-angle is high. X sits within the much harder to see 71km F, a heavily eroded outline which also encompasses E and D.
To the west lies 41km Rothmann, another prominent crater with complex and wide inner terraces. These lead to a small flat floor area with an offcentred, twin-peaked mountain complex. 45km Stiborius lies to Piccolomini’s south and isn’t dissimilar in appearance to Rothmann. A similar situation occurs to the east with 50km Neander, although this crater is defined by 11km Neander A positioned inside the northwest rim wall of its primary.
The most prominent neighbour is the impressive walled plain of Fracastorius, 260km north of Piccolomini. Fracastorius is located on the southern edge of Mare Nectaris and has become flooded with lava from the mare, the northern section of the crater being absent from view. The location of Fracastorius means that when the terminator is close enough to show it off at its best, Piccolomini will be optimally illuminated too.