Moon Phases
This interactive simulator explores Moon Phases in Astronomy & The Sky. Sun–Earth–Moon geometry and synodic cycle; lit fraction from phase angle. Use the controls to change the scenario; watch the visualization and any graphs or readouts to connect the model with lectures, labs, and homework.
Who it's for: Suited to beginners and first exposure to the topic. Typical context: Astronomy & The Sky.
Key terms
- moon
- phases
- moon phases
- astronomy
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
More from Astronomy & The Sky
Other simulators in this category — or see all 22.
Solar Eclipse Geometry
Sun–Moon–Earth: angular sizes, umbra and penumbra cones, orbit tilt.
Lunar Eclipse Geometry
Sun–Earth–Moon: Earth’s shadow on the Moon; total, partial, and penumbral (schematic colors).
Moon: Tidal Locking
Synchronous rotation: same lunar face toward Earth as it orbits.
Mars Retrograde Loop
Earth overtakes Mars: apparent backward loop among the stars (schematic).
Sidereal vs Solar Day
Why noon returns after slightly more than 360° of rotation (~4 min shorter sidereal day).
Axial Precession
Spin axis slowly cones; ~26 kyr cycle changes the pole star (schematic).