Moon Phases: Light, Not Shadow
beta readiness: candidate EarthSky Both 8 min
Beta demo with strong behavior and test coverage; final parity and launch-gate signoff pending.
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Predict
Predict
If the Moon were always opposite the Sun in the sky, what phase would you always see?
Play
Play
- Move the phase angle slider and describe what changes on the Moon’s face.
- Find the angle where the Moon looks half lit.
- Find the angles where the Moon looks fully dark and fully lit.
Explain
Explain
Use the idea of “illuminated fraction” to explain why the Moon looks different at different angles.
Learning goals
- Explain why the Moon has phases using the Sun–Earth–Moon geometry.
- Connect phase angle to the fraction of the Moon that appears lit.
- Distinguish illuminated fraction from how much of the Moon you can see.
Misconceptions targeted
- Phases are caused by Earth’s shadow.
Model notes
- This pilot visualization is a simplified 2D aid; it is not a full 3D rendering.
- Angle here is a proxy for Sun–Moon–Earth geometry; details will be refined in the full version.
About this demo
A short, interactive model for relating phase angle to what fraction of the Moon appears illuminated.