march: lunar farside
The Moon - like many other bodies in the solar system - has captured rotation. Its revolution around the Earth is (on average) exactly synchronous with its rotation on its axis, so from the Earth we always see the same half of its surface. More accurately we see nearly 60%, because of libration. Only 30 men have seen the remainder - the astronauts of Apollo missions 8 to 17.
This image, from the Apollo 16 mapping camera, shows how surprisingly different the two sides are. Almost all of the smooth maria are on the nearside, whilst the farside is rough and heavily cratered. On the left of the image is the Mare Crisium, to its right is the Mare Marginus, and below it the Mare Smythii: all nearside features. To the right of these is the farside, where the only dark feature visible is the flooded crater Lomonosov (above and to the right of Mare Marginus).