code: public static double[] calcNormalSunVector( double[] sunVector ) {
          double[] normalSunVector = new double[3];
          normalSunVector[2] = Math.sqrt(Math.pow(sunVector[0], 2) + Math.pow(sunVector[1], 2));
          normalSunVector[0] = -sunVector[0] * sunVector[2] / normalSunVector[2];
          normalSunVector[1] = -sunVector[1] * sunVector[2] / normalSunVector[2];
          return normalSunVector;
      }
docs: Calculating the normal to the sun vector.
  
  @param sunVector
  @return