The far side of the Moon, also called the dark side of the Moon, is the hemisphere of the Moon that faces away from Earth; the opposite hemisphere being the near side. Due to tidal locking, the time it takes for the Moon to orbit the Earth once is equal to the time it takes for the Moon to rotate once, thus, the far side of the Moon never fully comes into view from Earth's surface. The far side has sometimes been called the "dark side of the Moon", where "dark" means "unseen" instead of "unilluminated" – despite a common misconception that the dark side of the Moon is so-called because it never receives light, each location on the Moon experiences two weeks of sunlight while the opposite location experiences night. The far side is actually more reflective than the near side, as it lacks the large areas of darker maria surface.
About 18 percent of the far side is occasionally visible from Earth due to oscillation and to libration. The remaining 82 percent remained unobserved until 1959, when it was photographed by the Soviet Luna 3 space probe. The Soviet Academy of Sciences published the first atlas of the far side in 1960. The Apollo 8 astronauts were the first humans to see the far side in person when they orbited the Moon in 1968. Compared to the near side, the far side's terrain is rugged, with a multitude of impact craters and relatively few flat and dark lunar maria ("seas"), giving it an appearance closer to other barren places in the Solar System such as Mercury and Callisto. It has one of the largest craters in the Solar System, the South Pole–Aitken basin.
