Rupes Recta is a linear fault, or 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...

, on the Moon

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...

, in the southeastern part of the Mare Nubium

Mare Nubium

Mare Nubium is a lunar mare in the Nubium basin on the Moon's near side. The mare is located just to the southeast of Oceanus Procellarum. The actual basin is believed to be of Pre-Nectarian system, with the surrounding basin material being of the Lower Imbrian epoch. The mare material is of the...

 at . The name is Latin for "Straight Fault", although it is more commonly called the Straight Wall. This is the most well-known escarpment

Escarpment

An escarpment is a steep slope or long cliff that occurs from erosion or faulting and separates two relatively level areas of differing elevations.-Description and variants:...

 on the Moon, and is a popular target for amateur astronomers.

When the sun illuminates the feature at an oblique angle at about day 8 of the Moon's orbit, the Rupes Recta casts a wide shadow that gives it the appearance of a steep cliff. The fault has a length of 110 km, a typical width of 2–3 km, and a height of 240–300 m. Thus although it appears to be a vertical cliff in the lunar surface, in actuality the grade of the slope is relatively shallow.

To the west of this escarpment

Escarpment

An escarpment is a steep slope or long cliff that occurs from erosion or faulting and separates two relatively level areas of differing elevations.-Description and variants:...

 is the crater Birt

Birt (crater)

Birt is a lunar impact crater located in the eastern half of the Mare Nubium and west of the Rupes Recta.Birt is a bowl-shaped formation with a raised rim, slightly slightly intersected along the southeast edge by the much smaller crater Birt A...

, which is about 10.5 miles in diameter. Also to the west is the Rima Birt 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...

. At the southern end is a group of hills often called the "Stag's-Horn Mountains", although this name is not officially recognized 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...

.

To the northeast is the crater Alpetragius

Alpetragius (crater)

Alpetragius is a lunar impact crater located on the eastern edge of Mare Nubium, to the southwest of the much larger crater Alphonsus. In the southeast is the prominent crater Arzachel, and to the west lies the flooded Lassell....

, and to the east is Thebit

Thebit (crater)

Thebit is a lunar impact crater located on the southeast shore of Mare Nubium. To the north-northwest is the crater Arzachel, and Purbach lies to the south-southwest. To the southwest is the flooded remnants of Thebit P, which is actually larger in diameter than Thebit itself.The rim of Thebit is...

.