solar_longitude
double lon = solar_longitude(t_u);
while (winter >= solar_longitude(midnight_in_china(day+1)))
double lon = solar_longitude(t_u);
double phi = mod_f(lunar_longitude(t) - solar_longitude(t), 360);
double lon = solar_longitude(t);
return invert_angular(solar_longitude, lambda, a, b);
double lon = solar_longitude(t);
lon = solar_longitude(tau);
double lambda = solar_longitude(t);
double lambda = solar_longitude(ut);
double lon = solar_longitude(t_u);
double solar_longitude(double t);