Galen is a small 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...

 that lies in the rugged region between the Montes Apenninus

Montes Apenninus

Montes Apenninus are a rugged mountain range on the northern part of the Moon's near side. They are named after the Apennine Mountains in Italy....

 range to the west and the Montes Haemus

Montes Haemus

Montes Haemus is a curving range of mountains that forms the southwestern edge of the Mare Serenitatis basin on the Moon. They form a less prominent mirror image of the Montes Apenninus range to the west, and curve up to nearly join at the northern end. The eastern edge terminates with the...

 in the east. It is located to the south-southeast of the crater Aratus

Aratus (crater)

Aratus is a small lunar impact crater located on the highland to the south and east of the rugged Montes Apenninus range. It is a circular, cup-shaped crater with a relatively high albedo. To the east is the Mare Serenitatis, and to the southwest is the somewhat larger crater Conon...

, a slightly larger formation. Further to the west is the crater Conon

Conon (crater)

Conon is a small but prominent lunar impact crater that lies in the eastern foothills of the Montes Apenninus mountain range. Just to the west of Conon is the long mountainous ridge named Mons Bradley...

, near the flanks of the Montes Apeninnus. Galen was previously designated Aratus A before being given a name by the IAU

International Astronomical Union

The International Astronomical Union IAU is a collection of professional astronomers, at the Ph.D. level and beyond, active in professional research and education in astronomy...

.

This is a circular crater with a bowl-shaped interior and a sharp rim that has not undergone significant erosion. The small interior floor has a lower albedo

Albedo

Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

than the surrounding walls.