Working definition
A calendar date and clock reading are labels that map to an instant only with a calendar, timezone history, offset policy, and fold or gap resolution. Astronomical work then converts among UTC, TAI, TT, UT1, and other scales using leap-second and Earth-orientation data.
Notation
instant = resolve(calendar, local time, zone, fold)TT = TAI + 32.184 sAssumptions
- Calendar system and timezone identifier are known.
- Leap-second and Earth-orientation tables are versioned.
- Ambiguous or nonexistent local times are resolved explicitly.
Invariants
- A resolved instant can be represented in multiple scales.
- Timezone display changes do not change the instant.
- Scale offsets follow their defining standards.
Reproducible procedure
- Resolve the civil timestamp to an instant.
- Convert with authoritative scale tables.
- Store input label, resolution decision, instant, scale, and data version.
Error and boundary controls
- Historical timezone records can be uncertain.
- UT1 prediction degrades beyond measured Earth orientation.
- Date-only records imply an interval, not an exact instant.
What this does not establish
A precise event time improves reproducibility but does not make a natal, corporate, or electional interpretation empirically valid.
Explicit applications
2 cross-domain bridges
Civil time to ephemeris time
Resolve a local civil label and map the instant to the scale required by an ephemeris.
Inputs
- local date and time
- IANA timezone
- fold or gap policy
Outputs
- UTC instant
- ephemeris-scale argument
- resolution audit
Transformation: Resolve the instant, then apply versioned leap-second and scale offsets.
Limit: Historical zone uncertainty can be wider than numerical precision.
Open connected system →Local sunrise and civil-day mapping
Map an instant to a locality-specific calendrical day under explicit sunrise and timezone rules.
Inputs
- observer location
- timezone history
- sunrise convention
Outputs
- local day label
- boundary instant
- uncertainty flag
Transformation: Resolve civil time and calculate the relevant local boundary.
Limit: Polar and near-boundary cases require an explicit fallback convention.
Open connected system →Authoritative references
- [1]Standards of Fundamental Astronomy · International Astronomical Union
Establishes: Authoritative algorithms and conventions for astronomical timescales, Earth orientation, reference systems, astrometry, and celestial-coordinate transformations.
Boundary: SOFA standardizes astronomical computation. It supplies no astrological symbols, meanings, auspiciousness judgments, or evidence of predictive validity.
- [2]JPL Horizons System · NASA Jet Propulsion Laboratory
Establishes: Ephemeris products and documented observer, target, timescale, coordinate, and output conventions for reproducible Solar System state and observable calculations.
Boundary: Ephemeris agreement validates positions under declared conventions; it does not validate downstream symbolic classifications or interpretations.