Regiomontanus is an ancient lunar
impact crater located in the southern highlands region to the southeast of
Mare Nubium. It is joined at the chaotic northern rim by the crater
Purbach, and to the south-southeast is
Walther.
The crater is heavily worn from impact erosion, and the rim is irregular, mountainous and distinctly oval in outline. The walls on the southern and western edges have been almost completely degraded. A prominent ridge lies off-center to the northwest, with the small crater Regiomontanus A at its summit. The crater floor is
lava-flooded, and has a number of small crater impacts.
The summit crater Regiomontanus A was once considered proof of
volcanic activity on the Moon. However this feature is actually an impact crater, and is offset slightly from the summit of the central peak.
Satellite craters
By convention these features are identified on lunar maps by placing the letter on the side of the crater mid-point that is closest to Regiomontanus.
References
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