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.
John Carroll (astronomer) Sir John Anthony Carroll {'1': ", '2': ", '3': ", '4': "} (8 January 1899 – 2 May 1974) was a British astronomer and physicist. In the 1920s he worked at the Solar Physics Observatory, Cambridge, UK with F.J.M. Stratton and Richard van der Riet Woolley. He made major technological advances, inventing a high resolution spectrometer, and (with C G Fraser) a "coronal camera".