/// <summary>
/// Calculates sun position for a given date and latitude/longitude.
/// </summary>
/// <param name="date"></param>
/// <param name="lat"></param>
/// <param name="lng"></param>
/// <returns></returns>
public static SunPosition GetSunPosition(DateTimeOffset date, double lat, double lng)
{
var lw = Constants.Rad * -lng;
var phi = Constants.Rad * lat;
var d = date.ToDays();
var sunCoords = Sun.GetEquatorialCoords(d);
var h = Position.GetSiderealTime(d, lw) - sunCoords.RightAscension;
var azimuth = Position.GetAzimuth(h, phi, sunCoords.Declination);
var altitude = Position.GetAltitude(h, phi, sunCoords.Declination);
return(new SunPosition(azimuth, altitude));
}
/// <summary>
/// Calculates illumination parameters of the moon.
/// Location is not needed because percentage will be the same for both Northern and Southern hemisphere.
/// 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"></param>
/// <returns></returns>
public static MoonIllumination GetMoonIllumination(DateTime date)
{
var d = date.ToDays();
const int sdist = 149598000; // distance from Earth to Sun in km
var sunCoords = Sun.GetEquatorialCoords(d);
var moonCoords = Moon.GetGeocentricCoords(d);
var phi = Math.Acos(Math.Sin(sunCoords.Declination) * Math.Sin(moonCoords.Declination) +
Math.Cos(sunCoords.Declination) * Math.Cos(moonCoords.Declination) *
Math.Cos(sunCoords.RightAscension - moonCoords.RightAscension));
var inc = Math.Atan2(sdist * Math.Sin(phi), moonCoords.Distance - sdist * Math.Cos(phi));
var angle = Math.Atan2(
Math.Cos(sunCoords.Declination) * Math.Sin(sunCoords.RightAscension - moonCoords.RightAscension),
Math.Sin(sunCoords.Declination) * Math.Cos(moonCoords.Declination) -
Math.Cos(sunCoords.Declination) * Math.Sin(moonCoords.Declination) *
Math.Cos(sunCoords.RightAscension - moonCoords.RightAscension));
var fraction = (1 + Math.Cos(inc)) / 2;
var phase = 0.5 + 0.5 * inc * (angle < 0 ? -1 : 1) / Math.PI;
return(new MoonIllumination(fraction, phase, angle));
}
