These three conspicuous ring mountains form one of the most distinctive groups. They are almost identically sized, but are very different ages, nicely illustrating the lunar erosion process. Compare the young, sharp Theophilus (northernmost, top right) with intermediate Cyrillus (centre) and the old Catharina, its outline dulled by eons of sharp temperature change and bombardment by meteorites and micrometeorites.
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.