Jansen (Moon)

Named after Janszoon, Zacharias Jansen - Dutch optician (1580-c. 1638).

Jansen is lunar crater in the north part of the Mare Tranquillitatis. It is located to the east-southeast of the crater Plinius. The rim is low and narrow, with a notch along the western edge. The interior is level, which may indicate it has been covered by lava. (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.