Typed astronomical time primitives.

The central type is [Time<S, F>] (default F = [J2000s]), where S is a [Scale] marker (TT, TAI, UTC, UT1, TDB, TCG, TCB) and F is a [TimeFormat] tag (JD, MJD, [J2000s], [Unix], [GPS]).

tempoch makes a few explicit modeling decisions:

• [Time<S, F>] is an instant on a scale-specific axis; F only types external views (raw(), conversion targets), not a second storage layout.

• Time arithmetic follows affine rules: instant minus instant yields a duration; shifting an instant by a duration yields another instant.

• Internal storage is always a compensated (hi, lo) pair of J2000-based seconds so large epoch values can retain small corrections and sub-second detail.

• JD, MJD, J2000s, Unix, and GPS are conversion targets, not alternate stored encodings.

• UTC keeps special civil semantics: it is stored as a continuous instant and interpreted through the active UTC-TAI table when civil labels are needed.

• [Time::new] builds from a raw scalar when F is InfallibleFormatForScale for S (NaN panics; ±∞ allowed at rest). POSIX [Unix] instants still use [Time::try_new] / [Time::try_new_with] because decoding depends on leap-second tables.

• [Time::try_new] / [Time::try_new_with] surface domain decode failures only (UTC policy, leap seconds, …); callers must not pass NaN.

• UTC: civil (chrono) and POSIX ([Unix]); TAI: GPS ([GPS])

• Unified targets: [Time::to], [Time::try_to], [Time::to_with]. Prefer try_to or to_with for [Unix] so positive leap-second instants are rejected when they are not representable as POSIX.

• [Time::to_j2000s], [Time::reinterpret], and aliases such as [crate::JulianDate].

• [JulianDate], [ModifiedJulianDate], [UnixTime], and [GpsTime] implement [Into] into default-tagged [Time<S>] / [Time<UTC>] / [Time<TAI>], so APIs such as Period::try_new accept encoded endpoints without spelling [Time::to_j2000s]. [J2000Seconds<S>] is already [Time<S>]; no conversion needed.

See [constats] for epoch [Time] helpers, day/second scratch constants, and offsets.

Module map

• [foundation]: shared sealed traits, typed constants, and error types.
• [model]: [Time], scale markers, and conversion targets.
• [format]: external format markers and format conversion traits.
• encoding: crate-local JD/MJD/J2000/Unix arithmetic helpers.
• [earth]: ΔT, EOP, and [TimeContext] Earth-rotation policy.
• [data]: runtime access to bundled and optionally refreshed time-data tables.
• [period]: interval and period-list algebra.
• [features]: optional serde/tagged/time-instant integration helpers.

Reference modules:

• [earth::delta_t]: piecewise ΔT (TT - UT1) model and modern tabular segment.
• [earth::eop]: public EOP sampling API over bundled IERS series.
• [earth::context]: immutable time-data snapshot plus conversion policy.