question: How is it possible that there is a side of the moon, “The Dark Side”, that we never see?
comment: The Moon does exactly one rotation per orbit: it rotates on its axis with the same period than it rotates around the earth. This means that the same side is pointed toward the earth at all time (and and that the other side is never visible from the ground). This is called [tidal locking]( URL_0 ) and is very common for moons that orbit close to their parent planet.
passages: Section::::Concept.
   Section::::Background.
   Section::::Recording.
   Section::::Legacy.
   Section::::Legacy.:Rankings.
   Section::::Recording.:Completion.
   Section::::Legacy.:Dark Side of the Rainbow.
   Section::::Content.
   The phrase "dark side of the Moon" does not refer to "dark" as in the absence of light, but rather "dark" as in unknown: until humans were able to send spacecraft around the Moon, this area had never been seen. While many misconstrue this to think that the "dark side" receives little to no sunlight, in reality, both the near and far sides receive (on average) almost equal amounts of light directly from the Sun. However, the near side also receives sunlight reflected from the Earth, known as earthshine. Earthshine does not reach the area of the far side that cannot be seen from Earth. Only during a full Moon (as viewed from Earth) is the whole far side of the Moon dark. The word "dark" has expanded to refer also to the fact that communication with spacecraft can be blocked while the spacecraft is on the far side of the Moon, during Apollo space missions for example.
   Section::::Differences.
  
  The two hemispheres of the Moon have distinctly different appearances, with the near side covered in multiple, large "maria" (Latin for 'seas,' since the earliest astronomers incorrectly thought that these plains were seas of lunar water).
   The far side of the Moon is the hemisphere of the Moon that always faces away from Earth. The far side's terrain is rugged with a multitude of impact craters and relatively few flat lunar maria compared to the near side. It has one of the largest craters in the Solar System, the South Pole–Aitken basin. Both sides of the Moon experience two weeks of sunlight followed by two weeks of night; even so, the far side is sometimes called the "dark side of the Moon", where "dark" is used to mean unseen rather than lacking sunlight.
   The most extreme cases are Saturn's moon Pan, which orbits within the rings at only 70% of its fluid Roche limit, as well as Neptune's moon Naiad. Naiad's density is unknown, so its precise Roche limit is also unknown, but if its density were below 1100 kg/m³ it would lie at an even smaller fraction of its Roche limit than Pan.
   As a result of the Moon's synchronous rotation, one side of the Moon (the "near side") is permanently turned towards Earth, and the other side, the "far side", mostly cannot be seen from Earth. This means, conversely, that Earth can be seen only from the near side of the Moon and would always be invisible from the far side.
   The Moon is in synchronous rotation as it orbits Earth; it rotates about its axis in about the same time it takes to orbit Earth. This results in it always keeping nearly the same face turned towards Earth. However, because of the effect of libration, about 59% of the Moon's surface can actually be seen from Earth. The side of the Moon that faces Earth is called the near side, and the opposite the far side. The far side is often inaccurately called the "dark side", but it is in fact illuminated as often as the near side: once every 29.5 Earth days. During new moon, the near side is dark.
   It has also been proposed that the differences between the two hemispheres may have been caused by a collision with a smaller companion moon that also originated from the Theia collision. In this model, the impact led to an accretionary pile rather than a crater, contributing a hemispheric layer of extent and thickness that may be consistent with the dimensions of the far side highlands. However, the chemical composition of the farside is inconsistent with this model.
   Section::::Recording.:Voices.
   In the 17th century, Giovanni Cassini observed that he could see Iapetus only on the west side of Saturn and never on the east. He correctly deduced that Iapetus is locked in synchronous rotation about Saturn and that one side of Iapetus is darker than the other, conclusions later confirmed by larger telescopes.
   Section::::Release.:Label.
   Section::::Packaging.
   After the daemon describes other daemons' behavior, she goes on to describe Levania. Levania is divided into two hemispheres called Privolva and Subvolva. The two hemispheres are divided by the divisor. Privolva never sees Earth (Volva), Subvolva sees Volva as their moon. Volva goes throughout the same phases as the actual Moon.
   The two hemispheres have distinctly different appearances, with the near side covered in multiple, large "maria" (Latin for 'seas,' since the earliest astronomers incorrectly thought that these plains were seas of lunar water). The far side has a battered, densely cratered appearance with few maria. Only 1% of the surface of the far side is covered by maria, compared to 31.2% on the near side. According to research analyzed by NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission, the reason for the difference is because the Moon's crust is thinner on the near side compared to the far side. The dark splotches that make up the large lunar maria are lava-filled impact basins that were created by asteroid impacts about four billion years ago. Though both sides of the Moon were bombarded by similarly large impactors, the near side hemisphere crust and upper mantle was hotter than that of the far side, resulting in the larger impact craters. These larger impact craters make up the Man in the Moon references from popular mythology.
   Around 1600, William Gilbert made a map of the Moon that names Mare Imbrium "Regio Magna Orientalis" (the Large Eastern Region). Michael van Langren's 1645 map named it "Mare Austriacum" (the Austrian Sea).
  
  Section::::Observation and exploration.
  
  Mare Imbrium is visible to the naked eye from Earth. In the traditional 'Man in the Moon' image seen on the Moon in Western folklore, Mare Imbrium forms the man's right eye.
  
  Section::::Observation and exploration.:Luna 17.
   The doorman of Abbey Road Studios, Gerry O'Driscoll, is heard speaking at 1:37, answering the question: "What is 'the dark side of the moon'?" with: "There is no dark side in the moon, really. Matter of fact, it's all dark. The only thing that makes it look light is the sun."
   Section::::Discovery.
  
  Thirty inner satellites are currently known, found orbiting around all four of the giant planets (Jupiter, Saturn, Uranus and Neptune). Because of their small size, and glare from the nearby planet, they can be very difficult to observe from Earth. Some, such as Pan and Daphnis at Saturn, have only ever been observed by spacecraft.
   BULLET::::- Unlike the Earth, which has only one natural satellite, Darkover has four moons, each a different color, which affect tidal forces and weather patterns. These are Liriel, Kyrrdis, Idriel, and Mormallor. It is thought that Mormallor may have been a passing asteroid that was captured by Darkover's gravity.
  