Nielsen (Moon)

Named after Axel Vilfrid Nielsen - Danish astronomer (1902-1970) and Harald Herborg Nielsen - American physicist (1903-1973).

Nielsen is a lunar impact crater on the Oceanus Procellarum. It is located north-east of Montes Agricola on the western hemisphere. To the east-southeast is the crater Wollaston. Nielsen is a bowl-shaped formation that lies astride a small ridge that runs north-northwestwards towards the Mons Rümker. (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.