68 lines
1.8 KiB
C++
68 lines
1.8 KiB
C++
// precession.h
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//
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// Calculate precession angles for Earth.
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//
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// Copyright (C) 2008, the Celestia Development Team
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// Initial version by Chris Laurel, claurel@gmail.com
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//
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// This program is free software; you can redistribute it and/or
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// modify it under the terms of the GNU General Public License
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// as published by the Free Software Foundation; either version 2
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// of the License, or (at your option) any later version.
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namespace astro
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{
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// PA and QA are the location of the pole of the ecliptic of date
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// with respect to the fixed ecliptic of J2000.0
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struct EclipticPole
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{
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double PA;
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double QA;
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};
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// piA and PiA are angles that transform the J2000 ecliptic to the
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// ecliptic of date. They are related to the ecliptic pole coordinates
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// PA and QA:
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// PA = sin(piA)*sin(PiA)
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// QA = sin(piA)*cos(PiA)
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//
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// PiA is the angle along the J2000 ecliptic between the J2000 equinox
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// and the intersection of the J2000 ecliptic and ecliptic of date.
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struct EclipticAngles
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{
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double piA;
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double PiA;
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};
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// epsA is the angle between the ecliptic and mean equator of date. pA is the
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// general precession: the difference between angles L and PiA. L is the angle
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// along the mean ecliptic of date from the equinox of date to the
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// intersection of the J2000 ecliptic and ecliptic of date.
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struct PrecessionAngles
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{
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double pA; // precession
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double epsA; // obliquity
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};
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struct EquatorialPrecessionAngles
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{
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double zetaA;
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double zA;
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double thetaA;
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};
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extern EclipticPole EclipticPrecession_P03LP(double T);
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extern PrecessionAngles PrecObliquity_P03LP(double T);
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extern EclipticPole EclipticPrecession_P03(double T);
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extern EclipticAngles EclipticPrecessionAngles_P03(double T);
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extern PrecessionAngles PrecObliquity_P03(double T);
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extern EquatorialPrecessionAngles EquatorialPrecessionAngles_P03(double T);
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};
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