What optical device is the Dutch scientist, after whom the lunar crater Jansen is named, credited for?
Jansen (crater) Jansen is a lunar crater in the north part of the Mare Tranquillitatis, named after Zacharias Janssen. It is located to the east-southeast of the crater Plinius. The rim of Jansen is low and narrow, with a notch along the western edge. The interior is relatively level, which may indicate it has been covered by lava. To the south-southwest a small but prominent crater lies on the crater floor, halfway between the center and the rim, further southeast is a small but prominent crater named Sinas.
Einstein (crater) Einstein is a large lunar crater that lies along the western limb of the Moon, making it difficult to observe from the Earth. The visibility of this formation is affected by libration effects, but even under the best conditions not much detail can be observed except from lunar orbit. Nearby craters of note include Moseley just to the north, Dalton along the eastern rim, Vasco da Gama just to the southeast, and Bohr to the south-southeast. The formation Vallis Bohr is visible to the south.