AstroUtils.Time (astro_utils v0.1.0)

Time-scale helpers for astronomical computation.

Julian centuries from J2000.0 is the standard time argument for polynomial expressions in celestial mechanics (Meeus, IERS, IAU). J2000.0 is the epoch JD 2451545.0 TT, i.e. 2000 January 1 at 12:00 TT.

This module only rescales a Julian Date; it does not convert between time scales. Converting UTC to TT (leap seconds plus the 32.184 s TAI offset) is the caller's responsibility.

Summary

Functions

julian_centuries(jd_tt)

Convert a Julian Date (TT) to Julian centuries elapsed since J2000.0.

Functions

julian_centuries(jd_tt)

@spec julian_centuries(number()) :: float()

Convert a Julian Date (TT) to Julian centuries elapsed since J2000.0.

This is the standard T argument used in Meeus polynomials, IERS Earth orientation series, and IAU precession/nutation models. Dates before J2000.0 give negative values; there is no clamping.

Examples

iex> AstroUtils.Time.julian_centuries(2451545.0)
0.0

iex> AstroUtils.Time.julian_centuries(2451545.0 + 36525.0)
1.0

iex> AstroUtils.Time.julian_centuries(2451545.0 - 36525.0)
-1.0