phaseAngleEq function

double phaseAngleEq(double ra, double dec, double delta, double ra0, double dec0, double r,)

Phase angle from equatorial coordinates.

ra, dec, delta are Moon's geocentric RA, Dec, and distance. ra0, dec0, r are Sun's geocentric RA, Dec, and distance. Distances must be in the same units.

Implementation

double phaseAngleEq(double ra, double dec, double delta,
    double ra0, double dec0, double r) {
  final cPsi = math.sin(dec0) * math.sin(dec) +
      math.cos(dec0) * math.cos(dec) * math.cos(ra0 - ra);
  final sPsi = math.sin(math.acos(cPsi));
  return math.atan2(r * sPsi, delta - r * cPsi);
}