Reiner is a
lunar impact crater
An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact crater ...
on the
Oceanus Procellarum, in the western part of the
Moon
The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width ...
. It has a nearly circular rim, but appears oval in shape due to foreshortening. The rim edge is well-defined and has not been eroded by impacts. In the midpoint of the irregular crater floor is a central peak. Outside the rim is a hummocky
rampart
Rampart may refer to:
* Rampart (fortification), a defensive wall or bank around a castle, fort or settlement
Rampart may also refer to:
* "O'er the Ramparts We Watched" is a key line from "The Star-Spangled Banner", the national anthem of the ...
that extends out across the mare for about half a crater diameter.
To the west-northwest of the crater on the Oceanus Procellarum is the unusual feature
Reiner Gamma, a fish-shaped surface marking of
ray-like material with a high
albedo.
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 Reiner.
References
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Impact craters on the Moon