A lovely day 12 moon shone high yesterday afternoon and as the sun set, I took the scope out to gaze and sketch for an hour.

The terminator crossed just to the west of craters Kepler and Marius, and they looked an interesting pair, so I made them my target.

Kepler, left, is 32km wide: not large but one of the most distinctive lunar sights by virtue of its extensive bright rays, visible with the naked eye. Retaining bright rays indicates a young age; indeed it is probably less than a billion years old making it one of the younger lunar craters of any size. The crater is surrrounded by hummocky terrain, and several smaller craters, and the larger Encke, to its south (ie. above) which looks flooded, hence must be older than the surrounding Oceanus Procellarum (indeed it’s dated as Imbrium (3.2-3.85 billion years old). On the right (west) is Marius (43km). Because it’s much less distinctive than Kepler, it’s stunning to find that Marius is larger. Wrinkle ridges run north and south of Marius, and they have a knobbly appearance, crossing as they do the extensive dome field of Marius Hills, to the west of Marius.   

Here’s a labelled version.

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