Module tt 

Terrestrial Time (TT) time scale.

TT is the modern successor to Ephemeris Time (ET) and Terrestrial Dynamical Time (TDT). It provides a uniform time scale for geocentric ephemerides and is the basis for planetary position calculations referenced to Earth’s center.

Relationship to TAI

TT differs from TAI by a fixed offset:

TT = TAI + 32.184 seconds

The 32.184s offset was chosen to maintain continuity with ET at the 1977 epoch.

Usage

use celestial_time::{JulianDate, TT};

// Create TT at J2000.0 epoch
let tt = TT::j2000();

// From calendar date
use celestial_time::scales::tt::tt_from_calendar;
let tt = tt_from_calendar(2000, 1, 1, 12, 0, 0.0);

// Parse from ISO 8601
let tt: TT = "2000-01-01T12:00:00".parse().unwrap();

// Julian centuries since J2000.0 (for precession/nutation)
let centuries = tt.centuries_since_j2000();

Precision

TT uses split Julian Date storage internally, preserving microsecond accuracy across the full date range. The centuries_since_j2000() method provides the T parameter used in IAU precession and nutation models.

Structs

TT

Terrestrial Time representation.

Functions

tt_from_calendar

Creates TT from calendar components.