//Maybe...http://answers.google.com/answers/threadview/id/782886.html
//https://en.wikipedia.org/wiki/Position_of_the_Sun
//https://en.wikipedia.org/wiki/Solar_azimuth_angle
//http://www.itacanet.org/the-sun-as-a-source-of-energy/part-3-calculating-solar-angles/
public double[] getZenithAndAzimuth(DateTime time, double longitude, double latitude, double timezone)
{
int daysInYear = 365;
if (DateTime.IsLeapYear(time.Year))
{
daysInYear = 366;
}
//radians
double fractionalYear = (2 * Math.PI / daysInYear) * (time.DayOfYear - 1 + ((time.Hour - 12) / 24));
//eqptime in Minutes
double eqtime = 229.18 * (0.000075 + 0.001868 * Math.Cos(fractionalYear) - 0.032077 * Math.Sin(fractionalYear) - 0.014615 * Math.Cos(2 * fractionalYear) - 0.040849 * Math.Sin(2 * fractionalYear));
//decl in Radians
double decl = 0.006918 - 0.399912 * Math.Cos(fractionalYear) + 0.070257 * Math.Sin(fractionalYear) - 0.006758 * Math.Cos(2 * fractionalYear) + 0.000907 * Math.Sin(2 * fractionalYear) - 0.002697 * Math.Cos(3 * fractionalYear) + 0.00148 * Math.Sin(3 * fractionalYear);
double time_offset = eqtime + 4 * longitude - 60 * timezone;
double tst = time.Hour * 60 + time.Minute + time.Second / 60 + time_offset; //Tst= true solar time
double ha = (tst / 4) - 180; //Solar Hour Angle in degrees
//Debug.Log(ha);
//Solar Zenith Angle, and solar azimuth angle in radians
double sza = Math.Acos(MathD.Sin(latitude) * Math.Sin(decl) + MathD.Cos(latitude) * Math.Cos(decl) * MathD.Cos(ha)); //Solar Zenith Angle in radians
double saa = -(Math.Acos(-(MathD.Sin(latitude) * Math.Cos(sza) - Math.Sin(decl)) / (MathD.Cos(latitude) * Math.Sin(sza))) - Math.PI); //Solar Azimuth Angle
//Wikiperdia solar azimuth angle
//double saa = Math.Acos(
// (Math.Sin(decl) * Math.Cos(latitude) - Math.Cos(ha) * Math.Cos(decl) * Math.Sin(latitude)) / Math.Sin(sza)
// );
double[] answer = new double[2];
answer[0] = MathD.RadianToDegree(sza);
answer[1] = MathD.RadianToDegree(saa);
if (ha < 0 || ha > 180)
{
//answer[0] *= -1;
answer[0] += 180;
}
Debug.LogFormat("Time: {0},\tZenith: {1},\tAzimuth: {2},\tHour Angle: {3}", time.ToString(), answer[0], answer[1], ha);
return(answer);
}