Hippalus the remnant of 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...

 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...

 on the eastern edge of Mare Humorum

Mare Humorum

Mare Humorum is a lunar mare. The impact basin it is located in is 825 kilometers across. It was not sampled by the Apollo program, so a precise age has not been determined. However, geological mapping indicates that it is intermediate in age between the Imbrium and Nectaris Basins, suggesting an...

. To the southeast is the crater Campanus

Campanus (crater)

Campanus is a lunar impact crater that is located on the southwestern edge of Mare Nubium. It forms a crater pair with Mercator just to the southeast. Along the southern rampart of Campanus is the small lunar mare named Palus Epidemiarum...

, and to the northwest is the small flooded crater Loewy

Loewy (crater)

Loewy is a small lunar crater that lies along the eastern rim of Mare Humorum, in the southwest part of the Moon's near side. This is a lava-flooded formation that lies to the southwest of the larger, lava-flooded crater Agatharchides...

.

The southwest rim of Hippalus is missing, and the crater forms a bay along the edge of 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...

. The surviving rim is worn and eroded, forming a low, circular mountain range. The lava

Lava

Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...

-flooded floor of Hippalus is bisected by a wide rille

Rille

Rille is typically used to describe any of the long, narrow depressions in the lunar surface that resemble channels. Typically a rille can be up to several kilometers wide and hundreds of kilometers in length...

belonging to the Rimae Hippalus. This rille follows a course to the south before curving gently to the southwest for a total length of 240 kilometers. The crater floor to the east of this rille is more rugged than the area in the western half.

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 Hippalus.

Hippalus	Latitude	Longitude	Diameter
A	23.8° S	32.8° W	8 km
B	25.1° S	30.1° W	5 km
C	24.1° S	30.5° W	4 km
D	23.6° S	31.9° W	24 km