is a small lunar crater
that lies to the southeast of the larger Joule crater
, on the far side
of the Moon
. The rim of Foster is slightly eroded, and the narrow inner walls slope directly down to the relatively dark interior floor. The rim has a small outward bulge along the southwest side. There is a small craterlet on the floor next to the northern rim. A tiny impact in the southeast part of the crater interior is surrounded by a small skirt of high albedo
material, producing a bright patch.
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 Foster crater.