Lunar phases and synchronous rotation
Phases change the visible illuminated fraction; they are not Earth's shadow moving across the Moon.
Key knowledge
Away from eclipse, sunlight illuminates about half of the Moon. Its phase describes the illumination pattern of the apparent lunar disk as the Sun–Earth–Moon geometry changes, including the waxing or waning orientation. The phase cycle is about 29.5 days, longer than its roughly 27.3-day orbit relative to distant stars. Approximately synchronous rotation keeps broadly the same lunar hemisphere facing Earth, while libration reveals somewhat more than half over time.
Conditions and scope
- Periods are approximate present-day means, not constants for every lunation or orbit.
- Synchronous rotation is rotation, not absence of it; illumination and the near/far-side distinction describe different things. Eclipse shadowing is a separate alignment event.
Sources · 1
References
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Evidence and review
Inspected NASA Moon Phases illumination/phase bodies, libration discussion and 27.3/29.5-day and synchronous-rotation notes. Excludes 'far side never visible' and 'Sun only Solar-System body emitting light' absolutes.
2026-10-10 · Independent Mathematics and Information editor (/root/core_math_information). Independent AI editorial review of this entry's statements, equations, applicability conditions and source coverage. Source checks apply to these claims within their stated limits.
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