The
near side of the Moon is the
lunar hemisphere that is permanently turned towards the
Earth, whereas the opposite side is the
far side of the Moon. Only one side of the
Moon is visible from Earth because the Moon rotates about its spin axis at the same rate that the Moon orbits the Earth, a situation known as
synchronous rotation or
tidal locking. The Moon is directly illuminated by the
Sun, and the cyclically varying viewing conditions cause the
lunar phases. The unilluminated portions of the Moon can sometimes be dimly seen as a result of
earthshine, which is sunlight reflected off the surface of the Earth and onto the Moon. Since the Moon's orbit is both somewhat elliptical, and inclined to its
equatorial plane,
librations allow up to 59% of the Moon's surface to be viewed from Earth (but only half at any instant from any point).