/// <summary>
/// Compute sun declination for given julian date.
/// </summary>
/// <param name="julianDate">
/// Julian date of sun declination to be computed.
/// </param>
/// <returns>
/// Sun declination for given julian date.
/// </returns>
internal static double ComputeSunDeclination(double julianDate)
{
var epochDaysFraction = ComputeEpochDaysFraction(julianDate);
var sunMeanAnomaly = ComputeSunMeanAnomaly(epochDaysFraction);
var sunMeanLongitude = ComputeSunMeanLongitude(epochDaysFraction);
var sunEclipticLongitude = ComputeSunEclipticLongitude(sunMeanLongitude, sunMeanAnomaly);
var eclipticMeanObliquity = ComputeEclipticMeanObliquity(epochDaysFraction);
return(AngleMath.InverseSineInDegree(AngleMath.SineOfDegree(eclipticMeanObliquity) * AngleMath.SineOfDegree(sunEclipticLongitude)));
}
/// <summary>
/// Compute solar time for given julian date, time fraction, angle, latitude and direction.
/// </summary>
/// <param name="julianDate">
/// Julian date of solar time to be computed.
/// </param>
/// <param name="timeFraction">
/// Time fraction of the day of solar time to be computed.
/// </param>
/// <param name="angle">
/// Sun's angle of solar time to be computed.
/// </param>
/// <param name="latitude">
/// Location's latitude.
/// </param>
/// <param name="direction">
/// <see cref="Direction" /> value which determine whether sun is before or after mid day.
/// </param>
/// <returns>
/// Solar time for given julian date, time fraction, angle, latitude and direction.
/// </returns>
internal static double ComputeSolarTime(double julianDate, double timeFraction, double angle, double latitude, Direction direction)
{
var sunDeclination = ComputeSunDeclination(julianDate + timeFraction);
var midDay = ComputeMidDay(julianDate, timeFraction);
var solarTime = 0.0666666666666667 *
AngleMath.InverseCosineInDegree((-AngleMath.SineOfDegree(angle) -
(AngleMath.SineOfDegree(sunDeclination) * AngleMath.SineOfDegree(latitude))) /
(AngleMath.CosineOfDegree(sunDeclination) * AngleMath.CosineOfDegree(latitude)));
return(midDay + (direction == Direction.CounterClockwise ? -solarTime : solarTime));
}
/// <summary>
/// Compute sun's right ascension for given mean obliquity and ecliptic longitude.
/// </summary>
private static double ComputeSunRightAscension(double eclipticMeanObliquity, double sunEclipticLongitude)
{
return(AngleMath.InverseTangent2InDegree(AngleMath.CosineOfDegree(eclipticMeanObliquity) * AngleMath.SineOfDegree(sunEclipticLongitude),
AngleMath.CosineOfDegree(sunEclipticLongitude)) /
15.0);
}
/// <summary>
/// Compute sun's ecliptic longitude for given mean longitude and mean anomaly.
/// </summary>
private static double ComputeSunEclipticLongitude(double sunMeanLongitude, double sunMeanAnomaly)
{
return(AngleMath.FixDegreesAngle(sunMeanLongitude +
(1.915 * AngleMath.SineOfDegree(sunMeanAnomaly)) +
(0.02 * AngleMath.SineOfDegree(2.0 * sunMeanAnomaly))));
}
/// <summary>
/// Compute sun's mean longitude for given J2000 epoch days and fraction.
/// </summary>
private static double ComputeSunMeanLongitude(double epochDaysFraction)
{
return(AngleMath.FixDegreesAngle(280.459 + (0.98564736 * epochDaysFraction)));
}
/// <summary>
/// Compute sun's mean anomaly for given J2000 epoch days and fraction.
/// </summary>
private static double ComputeSunMeanAnomaly(double epochDaysFraction)
{
return(AngleMath.FixDegreesAngle(357.529 + (0.98560028 * epochDaysFraction)));
}
