Figure: Lunar tidal locking illustrated and explicated

Image 1 Caption: A not-to-scale cartoon illustrating the tidal locking of the Moon to the Earth.

Further explication:

1. The sizes of and distances between the objects are not-to-scale.

2. The shown orbital motion is relative to the center of the Earth, and so is only approximately relative to the center of mass of the center-of-mass inertial frame of Earth-Moon system which is the "true" orbital motion. Recall, center-of-mass inertial frames are NOT in rotation relative to the observable universe.

   Hereafter, by rotation, we mean rotation relative to the observable universe.

3. Image 1 is the FACTUAl case of a tidally locked Moon orbiting the Earth.

4. Tidally locked means the Moon's axial rotation rate is driven by the Earth's tidal force on the Moon to be equal its orbital rotation rate EXACTLY on average. In preserving exact equality on average, the tidal force is acting as a restoring force. For an explication of the physical origin of tidal locking, see Moon file: tidal_locking_origin.html.

5. Tidal locking implies the Moon turns one side to the Earth always as shown in Image 1. The side of the Moon we see from the Earth is the near side of the Moon. The side of the Moon we do NOT see from the Earth is the far side of the Moon.

6. Because of the lunar libration, we do see a 59 % of the Moon's surface from the Earth (see Wikipedia: Tidal locking: Occurrence: Earth's Moon), but only about 50 % at one time, of course. For a brief explication of the lunar libration, see Moon file: moon_lunar_tidal_locking_libration.html.

   

7. Image 2 Caption: In Image 2, we see four sides of the Moon: near, east, far, and west. If you look down on the Moon from north celestial pole (NCP), counterclockwise is east and the east side is eastward of the near side, and so is the east side in that sense. Similarly, clockwise is west and the west side is west of the near side, and so is the west side in that sense.

8. Counterfactually, if the Moon did not rotate relative to the observable universe, an observer on Earth would see all sides of the Moon cycling past with a period of the mean lunar sidereal month 27.321661547 days (J2000) ≅ 27.32166 days (to 7 digits) ≅ 27.3 days which is the true orbital period of the Moon relative to the observable universe.

   Of course, an Earth observer's view of the Moon in the counterfactual case would still be limited by the lunar phases just as in the factual case.