Alder 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 ...
that is located in the
southern hemisphere on the
far side 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 of ...
. It is located in the
South Pole-Aitken basin
South is one of the cardinal directions or compass points. The direction is the opposite of north and is perpendicular to both east and west.
Etymology
The word ''south'' comes from Old English ''sūþ'', from earlier Proto-Germanic ''*sunþaz ...
, and lies to the southeast of the crater
Von Kármán. Southeast of Alder is
Bose, and to the south-southwest lies
Boyle.
The inner wall of Alder is rough and slightly
terraced
In agriculture, a terrace is a piece of sloped plane that has been cut into a series of successively receding flat surfaces or platforms, which resemble steps, for the purposes of more effective farming. This type of landscaping is therefore ...
, with the material scattered across the edges of the otherwise relatively flat interior floor. There are several low central ridges lying along a band from the midpoint toward the eastern rim. A small crater lies on the eastern inner slopes. The crater is otherwise free of significant impacts within the rim.
Alder is associated with the only area in the basin not dominated by the
pyroxene rocks typical of lunar lowlands. This ''alder ejecta'' area is on
spectrographic evidence instead principally
anorthosite
Anorthosite () is a phaneritic, intrusive igneous rock characterized by its composition: mostly plagioclase feldspar (90–100%), with a minimal mafic component (0–10%). Pyroxene, ilmenite, magnetite, and olivine are the mafic minerals most ...
rock, typical of the lunar highlands.
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 Alder.
References
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External links
* (This article on South Pole-Aitken (SPA) basin mentions Alder crater.)
{{Craters on the Moon: A–B
Impact craters on the Moon