This is another of the great landmark crater groups. The large walled plain Ptolemaeus (or Ptolemy, to give it its more familiar English name) has a distictly hexagonal appearance. Apart from the conspicuous Ptolemaeus A, its interior appears featureless, suggesting that it has been flooded with lava. In fact, on closer inspection there are many smaller craters inside. The selenographer Ralph Baldwin counted nearly 200 using the Lick Observatory's 36 inch refractor.
Photo: Thierry Legault. The full size original of this and other high definition lunar images may be seen at his High Resolution CCD Imaging site.