// MeanObliquity returns mean obliquity (ε₀) following the IAU 1980
// polynomial.
//
// Accuracy is 1″ over the range 1000 to 3000 years and 10″ over the range
// 0 to 4000 years.
func MeanObliquity(jde float64) unit.Angle {
// (22.2) p. 147
return unit.AngleFromSec(base.Horner(base.J2000Century(jde),
unit.FromSexaSec(' ', 23, 26, 21.448),
-46.815,
-0.00059,
0.001813))
}
// MeanObliquityLaskar returns mean obliquity (ε₀) following the Laskar
// 1986 polynomial.
//
// Accuracy over the range 1000 to 3000 years is .01″.
//
// Accuracy over the valid date range of -8000 to +12000 years is
// "a few seconds."
func MeanObliquityLaskar(jde float64) unit.Angle {
// (22.3) p. 147
return unit.AngleFromSec(base.Horner(base.J2000Century(jde)*.01,
unit.FromSexaSec(' ', 23, 26, 21.448),
-4680.93,
-1.55,
1999.25,
-51.38,
-249.67,
-39.05,
7.12,
27.87,
5.79,
2.45))
}