From wikipedia:
Janssen is an ancient
impact crater located in the highland region near the southeastern
lunarlimb. The entire structure has been heavily worn and is marked by many lesser crater impacts. The outer wall is breached in multiple locations, but the outline of the crater rim can still be observed. The wall forms a distinctive
hexagonal shape upon the rugged lunar surface, with a slight curvature at the
vertices.The crater is named after French astronomer
Pierre Jules César Janssen.
[1]The prominent crater
Fabricius lies entirely within the outer wall, in the northeast
quadrant of the floor. A number of other lesser, but still notable craters mark the crater floor. Connected to the northeast rim is
Metius, and to the north is the heavily worn
Brenner. Southeast of Janssen are the co-joined craters
Steinheil and
Watt. Astride the southwest wall is the smaller
Lockyer. Further to the east, although appearing nearby due to elongation, is the huge
Vallis Rheita.In the southern two-thirds of Janssen can be discerned the remains of a large,
concentric crater, the wall of which is overlaid by Fabricius. The floor of this inner depression contains a
rille system named the Rimae Janssen. The rille curves from the rim of Fabricius to the southeast of the outer wall of Janssen, extending for a distance of up to 140 kilometers.
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