Regiomontanus (Moon)

Named after Muller, Johann Regiomontanus - German astronomer, mathematician (1436-1476).

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. (wikipedia entry)

A crater is a circular depression likely created by an impact event. On the Moon they are named after deceased scientists, polar explorers, astronauts or cosmonauts.