Rupes Altai is an 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:...

 in the lunar surface that is located in the southeastern quadrant of 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...

's near side. It is named for the Altai Mountains in Asia

Asia

Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...

. The selenographic coordinates of this feature are , and it has a length of about 427 km.

The southeastern end of the cliff terminates along the western edge of the crater Piccolomini

Piccolomini (crater)

Piccolomini is a prominent lunar impact crater located in the southeastern sector of the Moon. The crater Rothmann lies to the west-southwest, and to the south is Stiborius. The lengthy Rupes Altai begins at the western rim of Piccolomini, curving to the northwest. The crater is named after 16th...

. It then arcs irregularly towards the north, climbing to heights of nearly a kilometer. The northern end of the arc is an irregular region with no clearly defined terminus, where it brackets the prominent craters Theophilus

Theophilus (crater)

Theophilus is a prominent lunar impact crater that lies between Sinus Asperitatis in the north and Mare Nectaris to the southeast. It partially intrudes into the comparably sized crater Cyrillus to the southwest. To the east is the smaller crater Mädler and further to the south-southeast is Beaumont...

, Cyrillus

Cyrillus (crater)

Cyrillus is a lunar impact crater located on the northwest edge of Mare Nectaris. Intruding into the northeast rim is the equally large, and younger crater Theophilus. To the south is another prominent crater named Catharina. Together these three craters form a prominent trio in the southeast...

, and Catharina

Catharina (crater)

Catharina is an ancient lunar impact crater located in the southern highlands. It lies in a rugged stretch of land between the Rupes Altai scarp to the west and Mare Nectaris in the east. To the west-northwest is the crater Tacitus, and the lava-flooded Beaumont lies to the east along the shore of...

. This cliff forms the southwestern rim of the Nectaris

Mare Nectaris

The Sea of Nectar is a small lunar mare or sea located between the Sea of Tranquillity and the Sea of Fecundity . Montes Pyrenaeus borders the mare to the west and the large crater near the south center of the mare is known as Rosse...

impact basin.

This feature is difficult to locate during the full moon when the sunlight is nearly overhead. It is best viewed when the terminator is nearby and the sunlight is arriving at a low angle.