Photography: The Face of the Moon

by Tony Hicks

(photograph taken by Tony Hicks)

Rupes Recta is a linear fault, or rille, on the Moon, in the southeastern part of the Mare Nubium22°06′S 7°48′.The name is Latin for "Straight Fault", although it is more commonly called the Straight Wall. This is the most well-known escarpment 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.