The Helmet (Oceanus Procellarum)

The Helmet is an informal term for a highland mass within southern Oceanus Procellarum on the near side of the Moon, southeast of the crater Herigonius. The astronauts of Apollo 16 used the term to refer to the feature during the mission.[1] The name derives from the roughly semicircular shape of the border of the feature, resembling a helmet. The feature is topographically higher and of a higher albedo than the surrounding mare lava plain.

Lunar Orbiter 4 image of the helmet

Apollo 16 image, facing south. This is Figure 28-10 of the Apollo 16 Preliminary Science Report, the caption of which is "Distinct color boundaries of highland mass in Oceanus Procellarum"

Two mountains within The Helmet are informally named Herigonius Eta (η) and Herigonius Pi (π). Eta is the larger mountain on the northern edge of the Helmet, and Pi is along the southwest edge.

The selenographic coordinates of this feature are 16.8° S, 31.6° W.