public static void GetSunRiseSet(TimeZoneInfo tz, DateTime dt, double longitude, double latitude, out float sunRiseStart, out float sunRiseEnd, out float sunSetStart, out float sunSetEnd)
{
// get julian day at noon
var utcNoon = TimeZoneInfo.ConvertTimeToUtc(new DateTime(dt.Year, dt.Month, dt.Day, 12, 0, 0, DateTimeKind.Unspecified), tz);
double jdayNoon = GetJulianDayFromGregorianDateTime(utcNoon);
float sunUpperLimb = -0.833f;
float sunLowerLimb = 3f; // more than lower limb at horizon to look better
// magic
double d = jdayNoon - 2451543.5;
double w = 282.9404 + 4.70935E-5 * d;
double e = 0.016709 - 1.151E-9 * d;
double M = Degrees.Normalize(356.0470 + 0.9856002585 * d);
double E = Degrees.Normalize(M + Radians.ToDegrees(e) * Degrees.Sin(M) * (1 + e * Degrees.Cos(M)));
double xv = Degrees.Cos(E) - e;
double yv = Degrees.Sin(E) * Math.Sqrt(1 - e * e);
double lon = Degrees.Atan2(yv, xv) + w;
double lat = 0;
double rasc, decl;
ConvertEclipticToEquatorial(jdayNoon, lon, lat, out rasc, out decl);
double Ls = Degrees.Normalize(w + M);
double GMST = Degrees.Normalize(Ls + 180);
double UTSunInSouth = Degrees.Normalize(rasc - GMST - longitude) / 15.0f;
var noonUtc = new DateTime(dt.Year, dt.Month, dt.Day, 12, 0, 0, DateTimeKind.Utc);
var offset = tz.GetUtcOffset(noonUtc);
double cosLHA = (Degrees.Sin(sunUpperLimb) - Degrees.Sin(latitude) * Degrees.Sin(decl)) / (Degrees.Cos(latitude) * Degrees.Cos(decl));
if (cosLHA < -1)
{
// never set
sunRiseStart = 0;
sunSetEnd = 24;
}
else if (cosLHA > 1)
{
// never rise
sunRiseStart = 24;
sunSetEnd = 0;
}
else
{
double LHA = Degrees.Acos(cosLHA);
double convert = LHA / 15f;
sunRiseStart = (float)(UTSunInSouth - convert + offset.TotalHours);
sunSetEnd = (float)(UTSunInSouth + convert + offset.TotalHours);
}
cosLHA = (Degrees.Sin(sunLowerLimb) - Degrees.Sin(latitude) * Degrees.Sin(decl)) / (Degrees.Cos(latitude) * Degrees.Cos(decl));
if (cosLHA < -1)
{
// never set
sunRiseEnd = 0;
sunSetStart = 24;
}
else if (cosLHA > 1)
{
// never rise
sunRiseEnd = 24;
sunSetStart = 0;
}
else
{
double LHA = Degrees.Acos(cosLHA);
double convert = LHA / 15f;
sunRiseEnd = (float)(UTSunInSouth - convert + offset.TotalHours);
sunSetStart = (float)(UTSunInSouth + convert + offset.TotalHours);
}
}
