Mare Smythii

2.0°N, 87.0°E

Mare Smythii, ‘Smyth Sea’, named after a prominent, 19-century amateur observer, is a circular mare on the Moon's eastern limb and appears, because of limb foreshortening, to be highly elliptical. It covers an area of just about 105 000 km2, and a significant portion lies on the Moon's farside. Successful observation is only possible under favourable libration angles, but it then presents some interesting features. The outer wall of the basin rises above the lunar horizon, and various lava flows are visible inside it. In the north and south, in particular, there are unusually dark lava surfaces, which, in the south, are associated with the 55 km-diameter, FFC-crater Kiess. Mare Smythii is one of the youngest impact basins and its average depth is about 5 km below the general level of the surrounding surface.

Mare Marginis

12.0°N, 88.0°E

Mare Marginis, ‘Marginal Sea’, is an irregularly shaped lava area, 360 km across (about 62 000 km2). The mare has a north-south orientation and extends onto the Moon's farside.

Mare Marginis lies to the north of Mare Smythii. On the border between the mare lie the two craters Neper and Jansky. Neper (8.8°N, 84.5°E) is a large crater, 137 km in diameter. The floor of the crater is flooded by very dark lava and there is 1 2 a visible central peak. Jansky (8.5°N, 89.5°E) has a diameter of 73 km. Both craters are visible under favourable libration conditions.