/// <summary>
/// Calculate orbital data for binary star.
/// </summary>
/// <returns>
/// <para>positionAngleDeg -- Position angle (degrees)</para>
/// <para>separationArcsec -- Separation of binary members (arcseconds)</para>
/// </returns>
public (double positionAngleDeg, double separationArcsec) BinaryStarOrbit(double greenwichDateDay, int greenwichDateMonth, int greenwichDateYear, string binaryName)
{
var binaryInfo = BinaryInfo.GetBinaryInfo(binaryName);
var yYears = (greenwichDateYear + (PAMacros.CivilDateToJulianDate(greenwichDateDay, greenwichDateMonth, greenwichDateYear) - PAMacros.CivilDateToJulianDate(0, 1, greenwichDateYear)) / 365.242191) - binaryInfo.EpochPeri;
var mDeg = 360 * yYears / binaryInfo.Period;
var mRad = (mDeg - 360 * (mDeg / 360).Floor()).ToRadians();
var eccentricity = binaryInfo.Ecc;
var trueAnomalyRad = PAMacros.TrueAnomaly(mRad, eccentricity);
var rArcsec = (1 - eccentricity * (PAMacros.EccentricAnomaly(mRad, eccentricity)).Cosine()) * binaryInfo.Axis;
var taPeriRad = trueAnomalyRad + binaryInfo.LongPeri.ToRadians();
var y = (taPeriRad).Sine() * ((binaryInfo.Incl).ToRadians()).Cosine();
var x = (taPeriRad).Cosine();
var aDeg = PAMacros.Degrees(y.AngleTangent2(x));
var thetaDeg1 = aDeg + binaryInfo.PANode;
var thetaDeg2 = thetaDeg1 - 360 * (thetaDeg1 / 360).Floor();
var rhoArcsec = rArcsec * (taPeriRad).Cosine() / ((thetaDeg2 - binaryInfo.PANode).ToRadians()).Cosine();
var positionAngleDeg = Math.Round(thetaDeg2, 1);
var separationArcsec = Math.Round(rhoArcsec, 2);
return(positionAngleDeg, separationArcsec);
}
