Changing views of the lit lunar hemisphere produce ordinary phases.
NASA explanation of illumination, phase order and the roughly 29.5-day cycle.
NASA · Moon phasesThe same Moon. A changing view.: sources & model
Move the Moon around Earth and compare two viewpoints at once. Make a crescent, then tilt the orbit to discover why an eclipse is a special alignment.
Scientific review · independent subject review pending
The source and model records are available for inspection. No external scientific reviewer has signed off yet.
moon-phases-1 · content 1 · setup format 1What supports the explanation?
Orbital tilt makes eclipses less frequent than every new or full Moon.
NASA alignment and shadow explanation.
NASA · EclipsesEarth mean radius is 6371.0084 km.
JPL astronomical parameters; representative model ratios are rounded.
JPL · Planetary parametersMoon mean radius is 1737.4 km.
JPL satellite physical parameters; volume-equivalent mean radius.
JPL · Moon radiusRepresentative lunar distance and size set the scale of the system.
Mean distance about 384400 km and mean radius about 1737.4 km; these are not a date-specific ephemeris.
NASA · Moon factsWhat this model assumes
- Circular teaching orbit and directional sunlight. Display sizes and distances are exaggerated independently of the alignment calculation.
- The Earth-view disk represents the same geocentric illumination geometry, without location, horizon orientation, surface texture or libration.
- “No alignment in this model” is not a real-world eclipse exclusion: finite-Sun penumbral overlap is outside the simplified check.
- Illuminated fraction: For a distant Sun, the illuminated disk fraction is (1+cos α)/2, where α is the Sun–Moon–observer angle at the Moon. The implementation derives this from the Moon direction. It is a geometric area fraction, not calibrated photographic brightness.
- The optical model has its own scale: The displayed Earth and Moon are enlarged for readability. The separate alignment check uses Earth radius 1, Moon radius 0.2727 and separation 60.3, based on representative NASA/JPL sizes and distance. Camera changes do not change those numbers.
- An opportunity is not a forecast: The alignment check uses parallel sunlight and projected disk overlap. A finite Sun makes real umbra and penumbra geometry more complex. This model does not classify total, partial or annular eclipses, predict dates, local visibility or durations. The phase cycle is about 29.5 days; the playback has no calendar.
What has been checked
Analytical reference cases, conservation or transition invariants, finite drawing commands, bounded setup parsing, discovery and route integrity are checked automatically. These checks do not establish anatomical fidelity, learner outcomes or browser/device compatibility. Independent subject review, learner trials, comprehensive accessibility review and browser video encoding checks remain pending.
Each source supports the associated claim. Sources do not certify this implementation or its visuals.
About the cover illustration
The topic card uses an AI-generated editorial illustration. It introduces the subject; it is not a validated anatomical reference or a measured landscape. The experiment’s diagrams, readouts and assumptions explain the model separately.
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