Eci SolarPosition::FindPosition(const Julian& j)
{
const double mjd = j.FromJan1_12h_1900();
const double year = 1900 + mjd / 365.25;
const double T = (mjd + Delta_ET(year) / kSECONDS_PER_DAY) / 36525.0;
const double M = Util::DegreesToRadians(Util::Wrap360(358.47583
+ Util::Wrap360(35999.04975 * T)
- (0.000150 + 0.0000033 * T) * T * T));
const double L = Util::DegreesToRadians(Util::Wrap360(279.69668
+ Util::Wrap360(36000.76892 * T)
+ 0.0003025 * T*T));
const double e = 0.01675104 - (0.0000418 + 0.000000126 * T) * T;
const double C = Util::DegreesToRadians((1.919460
- (0.004789 + 0.000014 * T) * T) * sin(M)
+ (0.020094 - 0.000100 * T) * sin(2 * M)
+ 0.000293 * sin(3 * M));
const double O = Util::DegreesToRadians(
Util::Wrap360(259.18 - 1934.142 * T));
const double Lsa = Util::WrapTwoPI(L + C
- Util::DegreesToRadians(0.00569 - 0.00479 * sin(O)));
const double nu = Util::WrapTwoPI(M + C);
double R = 1.0000002 * (1 - e * e) / (1 + e * cos(nu));
const double eps = Util::DegreesToRadians(23.452294 - (0.0130125
+ (0.00000164 - 0.000000503 * T) * T) * T + 0.00256 * cos(O));
R = R * kAU;
Vector solar_position = Vector(R * cos(Lsa),
R * sin(Lsa) * cos(eps),
R * sin(Lsa) * sin(eps),
R);
return Eci(j, solar_position);
}
