Lunar eclipse calculation reference
How Maha calculates the Lunar eclipse as Full Moon entering Earth’s penumbral or umbral shadow, preserving UTC, phase direction, event type, location dependence, and uncertainty.
Timing reference · released 2026-08-18
Event definition
The Lunar eclipse is defined by a Sun–Moon phase-angle condition centered on near 180°. Penumbral, partial, and total classifications require shadow geometry beyond the ordinary Full Moon root.
Reproducible calculation
Search for the supporting syzygy, compute the Moon’s relation to its orbital nodes and the relevant shadow or observer geometry, classify the event, and refine contact times. Preserve geocentric event time separately from local visibility and contact circumstances.
Required inputs
- UTC search interval
- Geocentric Sun and Moon state
- Phase-angle and root convention
- Observer or shadow geometry and eclipse classification method
Maha convention
Maha records the Lunar eclipse instant as celestial geometry before deriving tithi, zodiac position, local date, or a tradition label. Tropical and sidereal Moon labels may differ, while the underlying Sun–Moon phase event remains one astronomical event.
Uncertainty and edge cases
Contact and visibility times can differ with ephemeris, correction model, timescale, and numerical tolerance. Local calendar date additionally depends on timezone; a date without UTC and zone provenance is not reproducible.
How reports may use this reference
Reports may show the exact Lunar eclipse root, local rendering, zodiac-frame labels, and separation from nearby chart points. Symbolic language requires a separately reviewed rule and must remain distinct from the phase calculation.
What this does not establish
The Lunar eclipse does not establish a beginning, culmination, crisis, release, or event outcome, and it is not evidence that a chart predicts reality.
Calculation and convention sources
Sources establish astronomical states or a declared chronology convention. They do not establish predictive meaning.
- Astronomy Engine
Don Cross (cosinekitty) · 2.1.19
Locally computed planetary longitudes, moon phases, eclipses, and search primitives used by Maha’s deterministic calculation layer.
Boundary: Library output is a computed astronomical result. Its reproducibility does not validate a symbolic or predictive meaning.
- Horizons System Manual
NASA/JPL Solar System Dynamics · 4.98d (2025-11-21)
Time-indexed solar-system states, observer centers, coordinate frames, apparent corrections, and output quantities used to verify planetary event searches.
Boundary: Horizons establishes astronomical states only when the complete query contract is retained; it supplies no astrological interpretation.
- Standards of Fundamental Astronomy
International Astronomical Union SOFA Board · 2023-10-11 release
Standard astronomical time-scale, precession, nutation, Earth-rotation, and coordinate-transformation algorithms.
Boundary: A standard transformation still requires declared inputs, ephemeris data, frame, origin, corrections, and software release.