public static MoonFracPhaseAngle GetMoonIllumination(DateTime dt)
{
double d = JulianDays(dt);
RaDec s = SunCoords(d);
MoonRaDecDist m = MoonCoords(d);
double sdist = 149598000; // distance from Earth to Sun in km
double phi = Math.Acos(Math.Sin(s.dec) * Math.Sin(m.dec) + Math.Cos(s.dec) * Math.Cos(m.dec) * Math.Cos(s.ra - m.ra));
double inc = Math.Atan2(sdist * Math.Sin(phi), m.dist - sdist * Math.Cos(phi));
double angle = Math.Atan2(Math.Cos(s.dec) * Math.Sin(s.ra - m.ra), Math.Sin(s.dec) * Math.Cos(m.dec) -
Math.Cos(s.dec) * Math.Sin(m.dec) * Math.Cos(s.ra - m.ra));
return(new MoonFracPhaseAngle {
fraction = (1 + Math.Cos(inc)) / 2, phase = 0.5 + 0.5 * inc * (angle < 0 ? -1 : 1) / PI, angle = angle
});
}
public static MoonAzAltDistPa GetMoonPosition(DateTime dt, double lat, double lng)
{
double lw = rad * -lng;
double phi = rad * lat;
double d = JulianDays(dt);
MoonRaDecDist c = MoonCoords(d);
double H = SiderealTime(d, lw) - c.ra;
double h = Altitude(H, phi, c.dec);
// formula 14.1 of "Astronomical Algorithms" 2nd edition by Jean Meeus (Willmann-Bell, Richmond) 1998.
double pa = Math.Atan2(Math.Sin(H), Math.Tan(phi) * Math.Cos(c.dec) - Math.Sin(c.dec) * Math.Cos(H));
h += AstroRefraction(h); // altitude correction for refraction
return(new MoonAzAltDistPa {
azimuth = Azimuth(H, phi, c.dec), altitude = h, distance = c.dist, parallacticAngle = pa
});
}
