d'Alembert is a large
lunar impact crater
An impact crater is a depression (geology), depression in the surface of a solid astronomical body formed by the hypervelocity impact event, impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal c ...
located in the
northern hemisphere
The Northern Hemisphere is the half of Earth that is north of the equator. For other planets in the Solar System, north is defined by humans as being in the same celestial sphere, celestial hemisphere relative to the invariable plane of the Solar ...
on the
far side of the
Moon
The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...
, to the northeast of the somewhat smaller walled plain
Campbell. Astride the southwest rim of d'Alembert is
Slipher. To the north is the crater
Yamamoto, and to the south-southwest lies
Langevin. This walled plain has the same diameter as
Clavius on the near side, making it one of the largest such formations on the Moon.
As with many lunar walled plains of comparable dimensions, the outer rim of this formation has been worn and battered by subsequent impacts. Besides Slipher, the most notable of these craters is d'Alembert Z intruding into the northern rim. There is also a small crater on the northwest inner wall that has a wide cleft in its eastern side, and a smaller crater along the southeastern inner wall. As eroded as the rim may be, its form can still be readily discerned as a roughly circular ridge line in the lunar terrain.
The interior floor of d'Alembert is a relatively level surface, at least in comparison with the rough terrain that surrounds the crater rim. It is marked with a number of small crater impacts, the largest being d'Alembert G and d'Alembert E toward the eastern rim. In the southwest, the floor is more irregular due to the outer
rampart
Rampart may refer to:
* Rampart (fortification), a defensive wall or bank around a castle, fort or settlement
Rampart may also refer to:
* LAPD Rampart Division, a division of the Los Angeles Police Department
** Rampart scandal, a blanket ter ...
and layers of ejecta from Slipher. A pair of shallow clefts in the floor surface radiate away from this crater, beginning near the midpoint of d'Alembert and reaching half-way toward the inner wall.
Satellite craters
By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to D'Alembert.
D'Alembert G is characterised by an extremely high
rockfall density by lunar standards.
References
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Impact craters on the Moon
{{Craters on the Moon: C-F