Which sentence supports the fact that we always see the same side of the moon? the moon takes about four weeks to rotate once on its axis and about the same time to orbit the earth. the gravitational effect of earth has slowed the rotational period of the moon to match its orbit. since the rotational period is exactly the same as the orbital period, the same portion of the moon always faces earth. as the moon orbits earth, the lit side that we see changes in size. these changes are called the lunar phases.