/// <summary>
/// Calculates solar position for a given location and point in time
/// </summary>
/// <param name="date">time and date calculate for</param>
/// <param name="latitude">latitude in degrees</param>
/// <param name="longitude">longitude in degrees</param>
/// <returns></returns>
public static SunPosition GetPosition(DateTime date, double latitude, double longitude)
{
double lw = Constants.Rad * -longitude;
double phi = Constants.Rad * latitude;
double d = Calendar.ToDays(date);
SunCoordinates c = Sun.Coordinates(d);
double H = Position.SiderealTime(d, lw) - c.RightAscension;
return(new SunPosition
{
Azimuth = Position.Azimuth(H, phi, c.Declination),
Altitude = Position.Altitude(H, phi, c.Declination)
});
}
/// <summary>
/// calculations for illumination parameters of the moon,
/// based on http://idlastro.gsfc.nasa.gov/ftp/pro/astro/mphase.pro formulas and
/// Chapter 48 of "Astronomical Algorithms" 2nd edition by Jean Meeus (Willmann-Bell, Richmond) 1998.
/// </summary>
/// <param name="date">time and date to calculate for</param>
/// <returns></returns>
public static MoonIllumination GetMoonIllumination(DateTime date)
{
var d = Calendar.ToDays(date);
var s = Sun.Coordinates(d);
var m = Moon.Coordinates(d);
const int sdist = 149598000; // distance from Earth to Sun in km
var phi = Math.Acos(Math.Sin(s.Declination) * Math.Sin(m.Declination) + Math.Cos(s.Declination) * Math.Cos(m.Declination) * Math.Cos(s.RightAscension - m.RightAscension));
var inc = Math.Atan2(sdist * Math.Sin(phi), m.Distance - sdist * Math.Cos(phi));
var angle = Math.Atan2(Math.Cos(s.Declination) * Math.Sin(s.RightAscension - m.RightAscension), Math.Sin(s.Declination) * Math.Cos(m.Declination) - Math.Cos(s.Declination) * Math.Sin(m.Declination) * Math.Cos(s.RightAscension - m.RightAscension));
var progressThroughCycle = 0.5 + 0.5 * inc * (angle < 0 ? -1 : 1) / Math.PI;
return(new MoonIllumination
{
Fraction = (1 + Math.Cos(inc)) / 2,
Phase = MoonPhaseMapper.FromProgressThroughCycle(progressThroughCycle),
Angle = angle
});
}
