17 November 2016 | Clavius Crater

Clavius Crater

Image credit: Luc Cathala | Click image to enlarge


Clavius is one of the largest crater formations on the Moon, and it is the third largest crater on the visible near side. It is located in the rugged southern highlands of the Moon, to the south of the prominent ray crater Tycho. The crater is named for the Jesuit priest Christopher Clavius, a 16th-century German mathematician and astronomer.

Due to the location of the crater toward the southern limb, the crater appears oblong due to foreshortening. Because of its great size, Clavius can be detected with the unaided eye. It appears as a prominent notch in the terminator about 1–2 days after the Moon reaches first quarter. The crater is one of the older formations on the lunar surface and was likely formed during the Nectarian period about 4 billion years ago.

Despite its age, however, the crater is relatively well-preserved. It has a relatively low outer wall in comparison to its size, and it is heavily worn and pock-marked by craterlets. The rim does not significantly overlook the surrounding terrain, making this a “walled depression”. The inner surface of the rim is hilly, notched, and varies in width, with the steepest portion in the south end. Overall the rim has been observed to have a somewhat polygonal outline.

The floor of the crater forms a convex plain that is marked by some interesting crater impacts. The most notable of these is a curving chain of craters that begin with Rutherfurd in the south, then arc across the floor in a counterclockwise direction forming a sequence of ever diminishing diameters. From largest to smallest, these craters are designated Clavius D, C, N, J, and JA. This sequence of diminishing craters has proved a useful tool for amateur astronomers who want to test the resolution of their small telescopes.

The crater floor retains a diminished remnant of a central massif, which lies between Clavius C and N. The relative smoothness of the floor and the low size of the central peaks may indicate that the crater surface was formed some time after the original impact.


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