fukushimaWilliams function

({double gamma, double phi, double psi}) fukushimaWilliams(
  1. double t
)

Fukushima–Williams angles (radians), eq. 5.40: γ̄, φ̄, ψ̄.

They relate the ecliptic of date directly to the GCRS (including the ICRS–J2000 frame bias), so no separate bias matrix is needed.

Implementation

({double gamma, double phi, double psi}) fukushimaWilliams(double t) => (
  gamma:
      _poly(t, [
        -0.052928,
        10.556378,
        0.4932044,
        -0.00031238,
        -0.000002788,
        0.000000026,
      ]) *
      arcsecond,
  phi:
      _poly(t, [
        84381.412819,
        -46.811016,
        0.0511268,
        0.00053289,
        -0.00000044,
        -0.0000000176,
      ]) *
      arcsecond,
  psi:
      _poly(t, [
        -0.041775,
        5038.481484,
        1.5584175,
        -0.00018522,
        -0.000026452,
        -0.0000000148,
      ]) *
      arcsecond,
);