MoonCycle.cc

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#include <utl/MoonCycle.h>
#include <utl/ModifiedJulianDate.h>


namespace utl {

  // "Mean" new moon of J2000 epoch: 6 Jan 2000 14:20 UT.
  const double kJ2000NewMoonMJD = 51549.59757;

  // Days in a mean synodic month (new moon to new moon period):
  const double kMeanSynodicMonth = 29.530589;


  double
  MoonCycle::GetLunation(const LunationType type, const LunationEpoch epoch)
    const
  {
    // Find the lunation (new moon cycle) relative to 6 Jan 2000 using the mean
    // synodic month.  This introduces a maximum discrepancy of +/-14 hours with
    // respect to the true lunation (checked between Jan 2000 - Dec 2030).
    double lunation =
      (ModifiedJulianDate(fTime) - kJ2000NewMoonMJD) / kMeanSynodicMonth;

    switch (epoch) {
      case eJan2000:      // Default: new moon of 6 Jan 2000 (first of J2000.0).
        break;
      case eJan2004:      // Subtract the 49 lunations bet. Jan 2000 and Dec 2003.
        lunation -= 49;
        break;
      default:
        break;
    }

    switch (type) {
      case eNewMoon:      // Fractional moon phase: 0 = New Moon.
        break;
      case eFirstQuarter: // Fractional moon phase: 0.25 = Full Moon.
        lunation -= 0.25;
        break;
      case eFullMoon:     // Fractional moon phase: 0.5 = Full Moon.
        lunation -= 0.5;
        break;
      case eLastQuarter:  // Fractional moon phase: 0.75 = Full Moon.
        lunation -= 0.75;
        break;
      default:
        break;
    }

    return lunation;
  }

}