public static double GetExcentricity(DateTime t)
{
int julian_date;
SolarCalculator.make_julian_day(t.Day, t.Month, t.Year, out julian_date);
double day_angle;//annual day angle
SolarCalculator.Day_Angle(julian_date, out day_angle);
double eccentricity;
SolarCalculator.corr_distance(day_angle, out eccentricity);
return(eccentricity);
}