Astronomical sources for the Moon tools
These references define the calculation implementation and the independent event-time checks. Links lead to the maintainers or public astronomical authorities rather than secondary summaries.
Calculation implementation
- Astronomy Engine 2.1.19
- The pinned JavaScript astronomy library used for Moon phase angle, illumination, and principal phase searches. Project source and documentation.
- TC39 Temporal polyfill 0.5.1
- Used to convert strict local calendar fields and IANA time-zone rules into UTC instants. Project source.
Independent definitions and event fixtures
- United States Naval Observatory: phases of the Moon
- Defines principal phases by 0°, 90°, 180°, and 270° excess apparent ecliptic longitude. Read the phase explanation.
- United States Naval Observatory: 2026 primary phase table
- Supplies the rounded-to-minute UTC fixtures used in automated tests. Open the 2026 table.
- NASA/JPL Solar System Dynamics
- A primary reference for planetary and lunar ephemeris systems and the Horizons service. Open JPL Horizons.
Source and version policy
Library versions and fixture sources are pinned in the repository. A calculation-engine update requires the external fixture tests and all invariant tests to pass before release. Display text must not claim a precision greater than the validated tolerance.
Read the full calculation methodology.