horizontalHourAngles function

Map<int, double> horizontalHourAngles(double phi)

Hour line angles for a horizontal sundial at latitude phi (radians).

Returns a map from hour offset (-6..6) to angle in radians from the noon line.

Implementation

Map<int, double> horizontalHourAngles(double phi) {
  final sPhi = math.sin(phi);
  final result = <int, double>{};
  for (var h = -6; h <= 6; h++) {
    if (h == 0) {
      result[h] = 0;
    } else {
      final ha = h * 15 * math.pi / 180; // hour angle in radians
      result[h] = math.atan(sPhi * math.tan(ha));
    }
  }
  return result;
}