00 · IN THREE MINUTES
The answer in three steps
- 1The Moon turns once on its axis in the same time that it circles Earth.
- 2Earth’s gravity raised a tidal bulge in the Moon; internal friction slowed the original spin until a stable resonance was reached.
- 3The far side receives sunlight too, and lets Earth see about 59 percent of the lunar surface over time.
01 · ROTATION IS THE REASON
Rotation is the reason
If the Moon did not rotate, every side would eventually face Earth during one orbit. Keeping the same hemisphere pointed inward requires exactly one axial turn per revolution.
02 · GRAVITY MAKES A BULGE
Gravity makes a bulge
Earth pulls slightly more strongly on the Moon’s near side than its far side. That difference stretches the Moon. When the bulge was not perfectly aligned, Earth’s torque changed the spin.
03 · FRICTION REMOVES SPIN ENERGY
Friction removes spin energy
Rock flexing inside the young Moon converted some organized rotational energy into heat. The orbit and spin exchanged angular momentum until the one-to-one state became stable.
Track the lunar marker: it keeps turning in space while the same face remains directed toward Earth.
Start
The marked face points toward Earth.
0° orbit04 · LOCKED DOES NOT MEAN FROZEN
Locked does not mean frozen
The Moon still travels around Earth and rotates relative to the stars. “” describes a matched pair of periods, not a stopped world.
05 · THE FAR SIDE IS NOT DARK
The far side is not dark
Both hemispheres have day and night. The far side is simply the hemisphere usually turned away from Earth. During a new moon it is mostly sunlit.
06 · WHY THE VIEW GENTLY ROCKS
Why the view gently rocks
The orbit is elliptical and the Moon’s axis is tilted. Libration changes our viewing angle, revealing slivers beyond the average edge and allowing us to see more than half the surface over a month.
07 · SOURCES AND EVIDENCE
Sources and evidence
The explanation follows the evidence chain below. Links open the original source.
- 01Tidal LockingOFFICIAL REFERENCE ↗
Supports a specific claim or evidence boundary used in this article.
- 02Top Moon QuestionsOFFICIAL REFERENCE ↗
Supports a specific claim or evidence boundary used in this article.
- 03Moon FactsOFFICIAL REFERENCE ↗
Supports a specific claim or evidence boundary used in this article.