TEC is an educational and comparative tool. Its calculations are grounded in real astronomical constants and formulae, but some outputs are intentionally approximate to keep the system lightweight and cross-platform. This page explains exactly what falls where.
What is computed precisely
Julian Day Number (JDN)
Converted from Gregorian dates using the Fliegel–Van Flandern algorithm, which is exact.
Tropical Sun longitude
Computed via the Meeus low-precision solar formula (Chapter 25). Accurate to ~0.01° for modern dates.
Moon longitude
Computed via Meeus Chapter 47 truncated series. Accurate to ~0.3° for modern dates.
New moon timing (H-CLET month starts)
Uses the Meeus Chapter 49 new moon series. Accurate to within ~1–2 minutes for modern dates.
Equinox / solstice timing
Bisection search on tropical sun longitude. Accurate to within ~minutes for the current millennium.
H-CLET civil date arithmetic
Pure JDN arithmetic once new moon instants are found — exact by construction.
IAU constellation boundaries
Lookup table from the 1930 IAU boundaries, applied directly in the tropical frame — exact within the table.
What is approximate
Lahiri ayanamsa (sidereal offset)
A simplified linear model (~23.853° + 50.29″/year). The IAU-standard Lieske et al. model is more precise; our value is accurate to ~0.1° for modern dates and degrades for dates >500 years from J2000.
Precessional age years
Derived from a mean-rate precession model (360° / 25,772 years). Earth's actual precession varies due to nutation and planetary perturbations. Age boundaries are approximate to within decades.
H-CLET epoch (9701 BCE)
Computed analytically. For deep historical dates, ephemeris precision degrades. The epoch is defined by intent (nearest new moon to the vernal equinox of the Holocene GSSP year) rather than a directly observed moment.
Lunar phase illumination
Computed from elongation as (1 - cos θ)/2. This is geometrically correct but does not account for lunar libration or limb effects.
Historical dates (pre-500 CE)
Accumulated calendar drift and the non-uniformity of Earth's rotation (ΔT) mean that H-CLET month start times may be off by a day or more for very ancient dates.
What is conceptual / systemic
The H-CLET calendar itself
H-CLET is a designed framework — a proposal for what a Holocene-anchored lunisolar calendar could look like. The rules (Metonic leap logic, month naming, Grand Era structure) are defined by the system, not observed from nature directly.
Precessional "ages"
The concept of astrological ages is cultural and interpretive. TEC presents them as a geometric consequence of the precession cycle using IAU constellation boundaries — a scientific framing, not an astrological claim.
Month names (Unasol, Duarc, etc.)
These are invented names defined by the H-CLET framework. They map to real lunations but the names themselves are a human convention.
How to interpret TEC outputs
- → For modern dates (1000 CE–3000 CE): trust moon phase and new moon timing to within 1–2 hours.
- → Sidereal constellation assignment is accurate to within ~1° for modern dates.
- → Precessional ages are directionally correct; treat year-within-age values as estimates ±decades.
- → For dates before 500 CE or after 3000 CE, treat all outputs as indicative rather than definitive.
- → The H-CLET calendar is an educational framework, not an official timekeeping standard.