Geological Chronicle
Arnold is an ancient lunar impact crater located in the north-northeastern part of the visible Moon, near the lunar limb. It lies to the northeast of Mare Frigoris and north of the crater Democritus, with the smaller crater Moigno to the west. This position gives the crater a notably oval appearance due to foreshortening, although the formation itself is actually relatively round.
The ancient rim has been worn and rounded by subsequent bombardment, and Patrick Moore described Arnold as "rather low-walled and obscure". The wall is relatively low along the eastern edge, while a southwestern gap is marked by the tiny crater Arnold J. The northern half of the rim is the most intact, joining the satellite crater Arnold A to the northeast.
The inner floor has been resurfaced, presumably by lava, leaving a relatively flat surface except for a number of tiny craterlets and the notable interior crater Arnold F in the northwest. If the crater once had a central peak, no sign of this feature now remains.