Geological Chronicle
Mach is a large lunar impact crater classified as a walled plain on the far side of the Moon, hidden from direct view from Earth. Measuring 174.97 kilometers in diameter, the formation displays an asymmetrical, pear-like outline marked by a prominent outward bulge to the northeast. Such bulges can form when an impact merges with a second crater. Its northern edge is the most worn and heavily overlain by subsequent impacts.
The interior floor and perimeter of Mach show substantial erosion from subsequent collisions. Along the eastern margin, the crater Harvey breaks across the rim and spills its outer rampart across the floor of Mach. The remainder of the interior floor is relatively level compared to the surrounding terrain, though small craters dot the northeastern bulge as well as the western and northwestern edges. Near the midpoint, a formation of central ridges rises from the floor, where the infrared spectrum of pure crystalline plagioclase has been identified.
Mach lies to the northeast of the Dirichlet–Jackson Basin, with Mitra along its western outer rim, Joule to the northeast, and Henyey to the southwest. Prior to being formally named in 1970 by the IAU, the crater was cataloged as Crater 236. The official designation honors Austrian physicist and philosopher Ernst Mach.