The long-awaited clear skies and the warm weather have clearly brought SPA members out to their telescopes and I have received images from Paul Brierly and Dave Finnigan. The seeing has not always been the best and this was the case on May 23rd when Paul acquired the image below. Nevertheless with the aid of a Baader 742nm IR Proplanet filter he produced a result with which he was happy and which shows a lot of detail.
North is to the bottom of this image which shows the prominent chain of craters dominated by the 153 km diameter Ptolemaeus, within which we see Ptolemaus A – also known as Ammonius. Nine kilometres in diameter, Ammonius is the largest of the numerous craters that can be seen on Ptolemaeus’ floor.
Immediately below Ammonius it is possible to make out Ptolemaeus B, most prominent of the many ‘ghost’ craters that exist within Ptolemaeus’ 2.4 km high walls. A low illumination is required to reveal these buried craters so they are best sought when the crater is close to the terminator.
The other craters in the chain are as follows:
Below Ptolemaeus is 41 km diameter Herschel, nearly 4 km deep with a prominent central peak. Adjoining Ptolemaeus to the south is Alphonsus, landing site of the U.S.A’s unmanned Ranger 9 in 1965. Above Alphonsus we see the 95 km Arzachel. This crater is well worth close inspection and high magnifications will show the rille to the east of its central mountain. 40 km Alpetragius nestles beside Alphonsus and Arzachel to the east.
North is top in Dave’s image, which features two of my lunar favourites. I have made several sketches of this distinctive pair which lie further south than Ptolemaeus, close to the craters Stofler and Faraday.
Maurolycus is some 114 km across and the peaks that you see in Dave’s image rise 4.7 km above its floor. The smaller Barocius (82 km) has its northern wall broken by Barocius B.