Lunar Libration — Why We See 59% of the Moon

Tidal locking is often described as "the Moon always shows Earth the same face," but that is only true on average. This simulator renders the real orbital mechanics behind that near-face: a moon locked into synchronous rotation spins at a perfectly constant rate, while its actual orbital speed varies with distance under Kepler's second law whenever the orbit is even slightly eccentric. The mismatch between a uniform spin and a non-uniform orbital angular speed produces libration in longitude, and a spin axis that stays roughly fixed in inertial space while the Moon's position sweeps around Earth produces libration in latitude. Together they rock the visible disk back and forth by several degrees each orbit — the real reason Earth-based observers have mapped close to 59% of the lunar surface with the naked eye, without any spacecraft ever needing to visit the far side to reveal that extra sliver. Adjust eccentricity and axial tilt to see the wobble grow or vanish, and switch to the orbit view to watch the Kepler orbit and the spin drift out of sync in real time.