Alpetragius is a lunar impact crater located on the east edge of Mare Nubium, to the southwest of the much larger Alphonsus crater. In the southeast is the prominent Arzachel crater, and to the west lies the flooded Lassell crater.

Alpetragius crater beside the larger Alphonsus

The most notable feature of this crater is the disproportionately large central peak, which forms a rounded rise that occupies almost the entire crater floor and rises to a height of 2.0 km. The rim has fine terraces that slope down to near the edge of the central rise along the south and east sides. The wall is nearly round, with slight protrusions on the north and west sides.

The outer rim is joined to the southwest rim of Alphonsus by a rise in the surface. An arc of craterous depressions from the south rim of Alphonsus crater curses to the west, dividing Alpetagnius from Arzachel crater. To the west-northwest is the crater-like outline of Alpetragius X, now flooded by the mare and overlain across the east by ejecta from Alpetragius.

Satellite craters

By convention these features are identified on Lunar maps by placing the letter on the side of the crater mid-point that is closest to Alpetragius crater.