2011-12-24 00:26:41 +00:00
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#include "SolarPosition.h"
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#include "Globals.h"
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#include "Util.h"
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#include <cmath>
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2012-10-11 18:52:51 +00:00
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Eci SolarPosition::FindPosition(const DateTime& dt)
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2011-12-24 00:26:41 +00:00
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{
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const double mjd = j.FromJan1_12h_1900();
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const double year = 1900 + mjd / 365.25;
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const double T = (mjd + Delta_ET(year) / kSECONDS_PER_DAY) / 36525.0;
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const double M = Util::DegreesToRadians(Util::Wrap360(358.47583
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+ Util::Wrap360(35999.04975 * T)
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- (0.000150 + 0.0000033 * T) * T * T));
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const double L = Util::DegreesToRadians(Util::Wrap360(279.69668
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+ Util::Wrap360(36000.76892 * T)
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+ 0.0003025 * T*T));
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const double e = 0.01675104 - (0.0000418 + 0.000000126 * T) * T;
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const double C = Util::DegreesToRadians((1.919460
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- (0.004789 + 0.000014 * T) * T) * sin(M)
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+ (0.020094 - 0.000100 * T) * sin(2 * M)
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+ 0.000293 * sin(3 * M));
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const double O = Util::DegreesToRadians(
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Util::Wrap360(259.18 - 1934.142 * T));
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const double Lsa = Util::WrapTwoPI(L + C
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- Util::DegreesToRadians(0.00569 - 0.00479 * sin(O)));
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const double nu = Util::WrapTwoPI(M + C);
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double R = 1.0000002 * (1 - e * e) / (1 + e * cos(nu));
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const double eps = Util::DegreesToRadians(23.452294 - (0.0130125
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+ (0.00000164 - 0.000000503 * T) * T) * T + 0.00256 * cos(O));
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R = R * kAU;
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Vector solar_position = Vector(R * cos(Lsa),
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R * sin(Lsa) * cos(eps),
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R * sin(Lsa) * sin(eps),
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R);
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return Eci(j, solar_position);
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}
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double SolarPosition::Delta_ET(double year) const
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{
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return 26.465 + 0.747622 * (year - 1950) + 1.886913
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* sin(kTWOPI * (year - 1975) / 33);
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}
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