Ptolemaeus crater near the centre of the near side of the lunar disk is 165-km-wide and exhibits a hexagonal shape typical of many large lunar impact craters. Total field of view is around 300 km. The main small crater on the floor of Ptolemaeus is the bowl-shaped Ammonius crater (9 km wide and 1.9 km deep). Fine craters are resolved scattered across the floor of Ptolemaeus that are around a kilometre diameter. To the upper right of Ptolemaeus is the large crater Alphonsus, whilst Herschel is the well-defined younger crater to the lower left.

There are two catena in this image. A catena is a linear array or chain of smaller craterlets that form when an incoming meteorite is broken apart by gravitational tidal forces just prior to impact, with each of the fragments impacting along a linear array. Catena Davy extends across the crater floor in the lower right-hand edge of the image, whilst a second unnamed catena can be seen in the upper-left quadrant of the image, skirting the right edge of Müller crater. A collapsed lava tube (rille) can be seen traversing the floor of Alphonsus in the upper right for some 50km in length.

The most interesting feature in this image, however, is the deep linear “chiselled” scour (one of many in the region) on the left side of Herschel, and extending half way up the image from the lower-left corner, and is at least a 100km in length. There are a whole series of these scours across the wider lunar landscape that all point radially toward the centre of the Mare Imbrium impact crater/mare basin outside the field of view. This impact was caused when a proto-planet from the asteroid belt collided with the moon during the Late Heavy Bombardment some 4 billion years ago (3922+/-12 million years from radiometric age dating). Not only was the Apennine Range (see previous post) thrown up along the SE margin of the impact basin, the outward hurled ejecta from the impact tore numerous chasms, tens to hundreds of kilometres long, deep into the lunar surface. The ~100-km-long chasm in this image (lower-left) which is around 8km wide and between 400-1000m deep, is just one of those scours, certainly a time of violence.

Skywatcher 8 inch/f5 Newtonian, Televue 2.5x, Focal length 2500mm, ASI1600mm Pro, NEQ6pro, ZWO red filter, 200 sub-frame stack.