/// <summary>
/// Creates a pair of equatorial coordinates with provided values of Right Ascension and Declination.
/// </summary>
/// <param name="alpha">Right Ascension value, in decimal degrees.</param>
/// <param name="delta">Declination value, in decimal degrees.</param>
public CrdsEquatorial(double alpha, double delta)
{
Alpha = Angle.To360(alpha);
Delta = delta;
}
// TODO: docs, tests
public static double LongitudeDifference(double eclipticalLongitudeSun, double eclipticalLongitudeBody)
{
double[] longitudes = new[] { eclipticalLongitudeBody, eclipticalLongitudeSun };
Angle.Align(longitudes);
return(longitudes[0] - longitudes[1]);
}
/// <summary>
/// Gets phase value (illuminated fraction of the disk).
/// </summary>
/// <param name="phaseAngle">Phase angle of celestial body, in degrees.</param>
/// <returns>Illuminated fraction of the disk, from 0 to 1.</returns>
/// <remarks>
/// AA(II), formula 48.1
/// </remarks>
// TODO: tests
public static double Phase(double phaseAngle)
{
return((1 + Math.Cos(Angle.ToRadians(phaseAngle))) / 2);
}
/// <summary>
/// Calculates heliocentrical coordinates of the planet using VSOP87 motion theory.
/// </summary>
/// <param name="planet"><see cref="Planet"/> to calculate heliocentrical coordinates.</param>
/// <param name="jde">Julian Ephemeris Day</param>
/// <returns>Returns heliocentric coordinates of the planet for given date.</returns>
public static CrdsHeliocentrical GetPlanetCoordinates(Planet planet, double jde, bool highPrecision = true)
{
Initialize(highPrecision);
const int L = 0;
const int B = 1;
const int R = 2;
int p = (int)planet - 1;
double t = (jde - 2451545.0) / 365250.0;
double t2 = t * t;
double t3 = t * t2;
double t4 = t * t3;
double t5 = t * t4;
double[] l = new double[6];
double[] b = new double[6];
double[] r = new double[6];
List <Term>[,,] terms = highPrecision ? TermsHP : TermsLP;
for (int j = 0; j < 6; j++)
{
l[j] = 0;
for (int i = 0; i < terms[p, L, j]?.Count; i++)
{
l[j] += terms[p, L, j][i].A * Math.Cos(terms[p, L, j][i].B + terms[p, L, j][i].C * t);
}
b[j] = 0;
for (int i = 0; i < terms[p, B, j]?.Count; i++)
{
b[j] += terms[p, B, j][i].A * Math.Cos(terms[p, B, j][i].B + terms[p, B, j][i].C * t);
}
r[j] = 0;
for (int i = 0; i < terms[p, R, j]?.Count; i++)
{
r[j] += terms[p, R, j][i].A * Math.Cos(terms[p, R, j][i].B + terms[p, R, j][i].C * t);
}
}
// Dimension coefficient.
// Should be applied for the shortened VSOP87 formulae listed in AA book
// because "A" coefficient expressed in 1e-8 radian for longitude and latitude and in 1e-8 AU for radius vector
// Original (high-precision) version of VSOP has "A" expressed in radians and AU respectively.
double d = highPrecision ? 1 : 1e-8;
CrdsHeliocentrical result = new CrdsHeliocentrical();
result.L = (l[0] + l[1] * t + l[2] * t2 + l[3] * t3 + l[4] * t4 + l[5] * t5) * d;
result.L = Angle.ToDegrees(result.L);
result.L = Angle.To360(result.L);
result.B = (b[0] + b[1] * t + b[2] * t2 + b[3] * t3 + b[4] * t4 + b[5] * t5) * d;
result.B = Angle.ToDegrees(result.B);
result.R = (r[0] + r[1] * t + r[2] * t2 + r[3] * t3 + r[4] * t4 + r[5] * t5) * d;
return(result);
}