/// <summary>
/// Calculates radius of Martian polar cap, in degrees of latitude,
/// depending on areocentric longitude of Sun.
/// </summary>
/// <param name="ls">Areocentric longitude of Sun</param>
/// <param name="cap">Northern or southern cap</param>
/// <returns>Radius of Martian polar cap, in degrees of latitude</returns>
/// <remarks>
/// The method is based on following simple assumtions:
/// 1. Polar cap size changes by sine law
/// 2. Radius of polar cap is between:
/// - 7...30 degrees for northern cap
/// - 0...30 degrees for southern cap
/// 3. Maximal width of NPC is around Ls = 345 degrees
/// 4. Maximal width of SPC is around Ls = 165 degrees
/// Refs:
/// https://www.sciencedirect.com/science/article/abs/pii/S0019103509003133
/// http://www.alpo-astronomy.org/jbeish/Observing_Mars_3.html
/// </remarks>
public static double MarsPolarCapRadius(double ls, PolarCap cap)
{
double LsMax = cap == PolarCap.Northern ? 345 : 165;
double Wmax = 30;
double Wmin = cap == PolarCap.Northern ? 7 : 0;
return(((-Math.Cos((ls + 180 - LsMax) / 180.0 * Math.PI) + 1.0) / 2.0) * (Wmax - Wmin) + Wmin);
}
private double Mars_PolarCap(SkyContext c, PolarCap cap)
{
double ls = c.Get(Mars_Calendar).Ls;
return(PlanetEphem.MarsPolarCapRadius(ls, cap));
}