Alpetragius is a lunar

Moon

The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

 impact crater

Impact crater

In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...

 located on the eastern edge of Mare Nubium

Mare Nubium

Mare Nubium is a lunar mare in the Nubium basin on the Moon's near side. The mare is located just to the southeast of Oceanus Procellarum. The actual basin is believed to be of Pre-Nectarian system, with the surrounding basin material being of the Lower Imbrian epoch. The mare material is of the...

, to the southwest of the much larger crater Alphonsus

Alphonsus (crater)

Alphonsus is an ancient impact crater on the Moon that dates from the immediate post-Nectarian era. It is located on the lunar highlands on the eastern end of Mare Nubium, west of the Imbrian Highlands, and slightly overlaps the crater Ptolemaeus to the north. The surface is broken and irregular...

. In the southeast is the prominent crater Arzachel

Arzachel (crater)

Arzachel is a relatively young lunar impact crater located in the highlands in the south-central part of the visible Moon, close to the zero meridian . It lies to the south of the crater Alphonsus, and together with Ptolemaeus further north the three form a prominent line of craters to the east of...

, and to the west lies the flooded Lassell

Lassell (lunar crater)

Lassell is a small lunar crater that is located in the eastern part of the Mare Nubium. It lies to the west of the crater Alpetragius, and southwest of 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—one-third the crater diameter—and rises to a height of 2.0 km. There is evidence that this peak has been enlarged through volcanic eruptions

Volcano

2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

, and there appears to be an eroded vent at its summit. The rim has fine terraces that slope down to near the edge of the central rise along the south and east sides. This outer 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 curves 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

Lunar mare

The lunar maria are large, dark, basaltic plains on Earth's Moon, formed by ancient volcanic eruptions. They were dubbed maria, Latin for "seas", by early astronomers who mistook them for actual seas. They are less reflective than the "highlands" as a result of their iron-rich compositions, and...

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.

Alpetragius	Latitude	Longitude	Diameter
B	15.1° S	6.8° W	10 km
C	13.7° S	6.1° W	2 km
G	18.2° S	6.5° W	12 km
H	18.0° S	6.0° W	5 km
J	18.0° S	5.7° W	4 km
M	16.5° S	3.2° W	24 km
N	16.7° S	3.8° W	11 km
U	17.7° S	5.1° W	14 km
V	18.1° S	5.8° W	17 km
W	17.9° S	6.0° W	27 km
X	15.6° S	5.7° W	32 km