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.
Steinheil (crater) Steinheil is a lunar impact crater that is located in the rugged highlands in the southeastern part of the Moon. It forms a prominent crater pair with the similar-sized Watt, which it partly overlies to the southeast. To the northwest is the large walled plain Janssen. Due to the location of this crater, it appears foreshortened when viewed from the Earth. It is from the Nectarian period, 3.92 to 3.85 billion years ago.