Posidonius (crater) - Definition

Posidonius is a lunar impact crater that is located on the western edge of Mare Serenitatis, to the south of Lacus Somniorum. The Chacornac crater is attached to the southeast rim, and to the north is Daniell crater.

The rim of Posidinius is shallow and obscured, especially on the western edge, and the interior has been overlaid by a lava flow in the past. The crater ramparts can still be observed to the south and east of the crater rim, and to a lesser degree to the north.

There is a smaller, semi-circular rim of a concentric, flooded crater within the main rim, offset toward the eastern edge. There is no central peak, but the floor is hilly and laced with a rille system named the Rimae Posidinius. The floor is also slightly buldged due to the past lava uplift, which also likely produced the complex of rilles.

The northeast rim is interrupted by the smaller crater Posidonius B. Within the crater rim, ofset just to the west of center is another smaller crater Posidinius A.

Satellite craters

By convention these features are identified on Lunar maps by placing the letter on the side of the crater mid-point that is closest to Posidonius crater.