MoonPhase C#

gistfile1.txt

namespace MoonPhase
{
    public class MoonPhase
    {
        static double MoonCycleLength = 29.53059;

        public int GetJulianDate(int day, int month, int year)
        {
            year = year - (12 - month) / 10;

            month = month + 9;

            if (month >= 12)
                month = month - 12;

            var k1 = (int)(365.25 * (year + 4712));
            var k2 = (int)(30.6001 * month + 0.5);
            
            // 'j' for dates in Julian calendar:
            var julianDate = k1 + k2 + day + 59;

            //Gregorian calendar
            if (julianDate > 2299160)
            {
                var k3 = (int)((year / 100 + 49) * 0.75) - 38;
                julianDate = julianDate - k3; //at 12h UT (Universal Time)
            }

            return julianDate;
        }

        public double GetMoonAge(int day, int month, int year)
        {
            double ip, age;

            int julianDate = GetJulianDate(day, month, year);

            ip = (julianDate + 4.867) / 29.53059;
            ip = ip - Math.Floor(ip);

            age = ip * MoonCycleLength + MoonCycleLength / 2;

            if (age > MoonCycleLength)
                age -= MoonCycleLength;

            return age;
        }
    }
}