Moon Phases
Interactive simulation — adjust parameters and watch the visualization update in real time.
How it works
The Moon’s phase depends on the angle between the Earth–Moon line and the direction to the Sun. After one synodic month (~29.5 days) the Moon returns to the same phase as seen from Earth. This page is a schematic diagram, not a planetarium ephemeris.
Key equations
visible lit fraction ∝ (1 − cos θ) / 2 (simplified)