This time we are again near the lunar terminator (the line that demarcates dawn or dusk when shadows are longer) in the central highlands near the zero meridian and looking almost directly down onto the lunar surface from our vantage point on earth. The earth-facing trio of large, aligned, ancient impact craters, from lower left to upper right, are Ptolemaeus, Alphonsus and Arzachel. The 4th crater in this “string-of-pearls” (Purbach) lies off the top-right corner.

Ptolemaeus is named after Claudius Ptolemy, known for his astronomical treatise the Almagest. Alphonsus and Arzachel have rilles along their upper-left crater floors as well as central peaks, whilst Ptolemaeus lacks a central peak, but appears to have a very faint rille along its lower-right crater floor.

In March 1965 the Ranger 9 spacecraft captured final images of the Moon before crashing into the 108-kilometer-wide Alphonsus crater (centre). The crater walls of Arzachel (middle of top-right quadrant) can be seen slumping inward.

Directly below Arzachel is the smaller crater Alpetragius (centre-right) with its unusual and proportionally large central dome that rises about 2 km above the crater floor. The similar-sized crater in the lower-left of the image, off the edge of Ptolemaeus, is Herchel.

The two craters in Mare Nubium (lower right) are Lassell and Davy, the latter just to the right of the Davy Catena. The large crater in the upper-left is Albategnus with the overlapping Klein crater on its right-side crater rim. The left side rim of Klein is likewise disrupted by an even younger and smaller crater.

Distributed linear gouges from the Mare Imbrium impact can be seen scouring the landscape.

Imaging: Skywatcher 8inch/f5 Newtonian, ASI1600mm Pro camera, TVue 2.5x Powermate, NEQpro6 mount, ZWO 36mm red filter.
Capture software: Sharpcap.
Processing: Autostakkert, Registrax, LR, TDN (Imaged from Lysterfield, Vic, 18-02-2034).