PABinary.cs

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using System;
using PALib.Data;
using PALib.Helpers;
 
namespace PALib;
 
public class PABinary
{
    public (double positionAngleDeg, double separationArcsec) BinaryStarOrbit(double greenwichDateDay, int greenwichDateMonth, int greenwichDateYear, string binaryName)
    {
        BinaryData binaryInfo = BinaryInfo.GetBinaryInfo(binaryName);
 
        double yYears = greenwichDateYear + (PAMacros.CivilDateToJulianDate(greenwichDateDay, greenwichDateMonth, greenwichDateYear) - PAMacros.CivilDateToJulianDate(0, 1, greenwichDateYear)) / 365.242191 - binaryInfo.EpochPeri;
        double mDeg = 360 * yYears / binaryInfo.Period;
        double mRad = (mDeg - 360 * (mDeg / 360).Floor()).ToRadians();
        double eccentricity = binaryInfo.Ecc;
        double trueAnomalyRad = PAMacros.TrueAnomaly(mRad, eccentricity);
        double rArcsec = (1 - eccentricity * PAMacros.EccentricAnomaly(mRad, eccentricity).Cosine()) * binaryInfo.Axis;
        double taPeriRad = trueAnomalyRad + binaryInfo.LongPeri.ToRadians();
 
        double y = taPeriRad.Sine() * binaryInfo.Incl.ToRadians().Cosine();
        double x = taPeriRad.Cosine();
        double aDeg = PAMacros.Degrees(y.AngleTangent2(x));
        double thetaDeg1 = aDeg + binaryInfo.PANode;
        double thetaDeg2 = thetaDeg1 - 360 * (thetaDeg1 / 360).Floor();
        double rhoArcsec = rArcsec * taPeriRad.Cosine() / (thetaDeg2 - binaryInfo.PANode).ToRadians().Cosine();
 
        double positionAngleDeg = Math.Round(thetaDeg2, 1);
        double separationArcsec = Math.Round(rhoArcsec, 2);
 
        return (positionAngleDeg, separationArcsec);
    }
}