Strawberry Full Moon Rises over Redonda Peak

The moon orbits the earth every 27.322 days.  It takes about the same time for the moon to rotate on its axis, 27 days. Gravitational forces between the earth and the moon result in torque on the moon resulting in its rotation period approaching its orbital period around the earth.  This effect is known as tidal locking⁽²⁾https://www.universetoday.com/128350/will-earth-lock-moon/.  Tidal locking is why we see the same side of the moon from the earth.   The moon does not appear to be spinning.  It appears to be stationary on its axis.  The earth and moon are in synchronous rotation⁽³⁾https://en.wikipedia.org/wiki/Synchronous_orbit.

The Dark Side of the Moon

What about the far side of the moon?  Pink Floyd’s famous album, “The Dark Side of the Moon“, hints to us that perhaps the side of the moon we do not see is “dark”.  A better name for that side of the moon that we do not see is, “The Far Side of the Moon”.   Since the moon rotates around its axis, even though it appears still to us, its entire surface receives almost the same amount of light from the sun.

The side of the moon facing the earth is brighter though due to light reflecting from the surface of the earth, known as earthshine. When the sun’s illumination of the earth as seen from the moon is full, a “Full Earth”, the amount of earthshine illuminating the surface of the moon facing the earth is about 34 times the amount of moonlight illuminating the earth during a full moon.

Earthshine is most clearly seen after dusk during the waxing crescent (in the western sky) and before dawn during the waning crescent (in the eastern sky).

When we take earthshine into account, the far side of the moon is actually the darker side of the moon.