double calcSunsetUTC(double JD, double latitude, double longitude)
{
double t = calcTimeJulianCent(JD);
// *** First pass to approximate sunset
double eqTime = calcEquationOfTime(t);
double solarDec = calcSunDeclination(t);
double hourAngle = calcHourAngleSunset(latitude, solarDec);
double delta = longitude - radToDeg(hourAngle);
double timeDiff = 4 * delta; // in minutes of time
double timeUTC = 720 + timeDiff - eqTime; // in minutes
double newt = calcTimeJulianCent(calcJDFromJulianCent(t) + timeUTC/1440.0);
eqTime = calcEquationOfTime(newt);
solarDec = calcSunDeclination(newt);
hourAngle = calcHourAngleSunset(latitude, solarDec);
delta = longitude - radToDeg(hourAngle);
timeDiff = 4 * delta;
timeUTC = 720 + timeDiff - eqTime; // in minutes
// printf("************ eqTime = %f \nsolarDec = %f \ntimeUTC = %f\n\n",eqTime,solarDec,timeUTC);
return timeUTC;
}
double calcSolarZenith(double latitude, double longitude, int year, int month, int day, int timeUTC){
double T, trueSolarTime, hourAngle, solarDec, csz, zenith, exoatmElevation, te, refractionCorrection;
T=jd2jcent(mdy2jd(year, month, day) + timeUTC/1440.0);
trueSolarTime = timeUTC + calcEquationOfTime(T) - 4.0 * longitude;
hourAngle = trueSolarTime / 4.0 - 180.0;
solarDec = calcSunDeclination(T);
csz = sin(deg2rad(latitude)) * sin(deg2rad(solarDec)) +
cos(deg2rad(latitude)) * cos(deg2rad(solarDec)) *
cos(deg2rad(hourAngle));
zenith=rad2deg(acos(csz));
exoatmElevation = 90.0 - zenith;
if (exoatmElevation > 85.0) {
refractionCorrection = 0.0;
} else {
te = tan(deg2rad(exoatmElevation));
if (exoatmElevation > 5.0) {
refractionCorrection = 58.1/te - 0.07/(te*te*te) +
0.000086/(te*te*te*te*te);
} else if (exoatmElevation > -0.575) {
refractionCorrection = 1735.0 + exoatmElevation*(-518.2 + exoatmElevation*(103.4 + exoatmElevation*(-12.79 + exoatmElevation*0.711)));
} else {
refractionCorrection = -20.774 / te;
}
refractionCorrection = refractionCorrection / 3600.0;
}
return zenith - refractionCorrection;
}
