Moonwatch

Sulpicius Gallus

SULPICIUS GALLUS IS a small, bowl-shaped crater close to the southwest border of the Mare Serenitatis. Despite its diminutive size, Sulpicius Gallus is quite prominent: it is bright and has a rim that rises above the surrounding floor of the lunar sea. Consequently, when the Sun is high in the lunar sky, the crater looks like a bright patch against the darker mare floor. When the Sun is low in the lunar dawn sky, Sulpicius Gallus casts a dramatic shadow across the mare which, at high magnification, shows the rim has somewhat jagged edges.

The closest part of the border of the Mare Serenitatis lies about 20km to the southwest of the crater. The mare boundary is marked by the curving mountain range Montes Haemus. This arcs along the southwest edge of Serenitatis, starting in the east to the north of crater Plinius (43km). The range curves up to the western edge of the mare, where it almost joins in a peak with the more dramatic Montes Apenninus, bordering the giant Imbrium Basin to the west.

The region southwest of Montes Haemus is a mixture of mountainous terrain and low regions that have been flooded by dark lava. These carry some odd names such as Lacus Odii (Lake of Hate), Lacus Felicitatis (Late of Happiness), Lacus Doloris (Lake of Sorrow) and Lacus Gaudii (Lake of Delight). There are so many lunar lakes here that it is a bit like the Moon’s version of the Lake District.

The region immediately west of Sulpicius Gallus contains a forking system of rilles known as Rimae Sulpicius Gallus. These require a 10-inch or larger scope to see well. The rilles start to the west of Sulpicius Gallus as a single crack in the lunar surface. As the crack heads west, it starts to curve to the northwest and splits into three. As it does so, it passes across a dark region of pyroclastic material laid down by volcanic activity. In fact this region is one of the largest pyroclastic deposits on the entire Moon.

A number of bright, young craters pockmark the area, one being Sulpicius Gallus M (5km), which lies on the southern edge of the dark pyroclastic region.

Under low illumination lots of subtle and interesting features appear. There are several domes here, such as Sulpicius Gallus 4 (16km) to the west of the main crater, and Sulpicius Gallus 2 (5km) to the east. A low illumination casting oblique light is required to spot them using a 8-inch or larger scope.

There’s a lovely wrinkle ridge known as Dorsum Buckland that runs for some distance roughly parallel with the Montes Haemus on the mare floor. Following the ridge west, where it passes north of Sulpicius Gallus, there’s a smaller ridge feature that appears to split and head north. This is known as Dorsum Von Cotta.

“Sulpicius Gallus is bright and has a rim that rises above the floor of the mare”