text: why the moon show the same face?   the answer is that the moon's period of revolution (one orbit around the earth) is the same as the moon's period or rotation (one spin around it's axis). the result is that the moon always keeps on side facing the earth.  this phenomena is called "tidal locking" and occurs because, while the moon generates tides in the earth, the earth also generates a tide in the moon (in the solid rock). the moon's tidal budge moves as the moon rotates. the energy for this, and the gravitational effects from the distortion, lead to a braking effect. the moon slows down its rotation until it is such that the buldge is on one side always faces the earth.  now the tidal bulge is stationary (facing the earth) and no more braking occurs.   this is also related to why there are lot more lunar mare on the near side than the far side. the moon's core is shifted slightly towards the earth, so it was easier for lava seas to form on the near side.  many other satellites are tidally locked to their planet. mercury is almost tidally locked to the sun.