March 16, 2020
Tiny Volcanic Features
Originally published October 3, 2010
image by Stefan Lammel, England
This excerpt from one of Stefan's large mosaics contrasts the northern Procellarum volcanic landscape with the crater scarred ejecta blanket of Sinus Iridum. The most conspicuous volcanic landform is the widespread and smooth plains of Oceanus Procellarum. But five smaller volcanic features are more fascinating. Easiest to see ae the two Gruithuisen domes (1) near center-right. These are steep-sided domes, and in this lighting the edges are bright and fibrous as if they were taffy and had been pulled up away from the mare surface. Right along the bottom center edge is a smaller smooth walled depression (2), presumably resulting from the covering of an impact crater by Procellarum's lavas - this looks like the saucers in Ptolemaeus. Harder to see near the middle of the image is a curved, rimless depression (3) which is the source area for the famous twisted rille best seen on orbital imagery. Moving up along the edge of ejecta blanket is the widest and most visible section of the Mairan Rille (4). Finally, at the top center is the strange volcano Mairan T (5). This is one of the larger volcanic cones on the Moon (7 km wide and 900 m high) and is unusual because of its steep sides. Unfortunately, the small size of these volcanic features makes them hard to image and nearly impossible to detect visually - I have only observed the Gruithuisen domes at the eyepiece.
04-Sept-10 03:58-05:12UT. 10in f4.8 Newtonian, Infinity 2-1M, 5x Powermate, Baader green filter, Avistack, PSE5, Focus Magic
Rükl plate 9