code: public function setDate($year, $month, $day)
      {
          $status = IAU::Cal2jd((int)$year, (int)$month, (int)$day, $djm0, $djm);
          $this->checkDate($status);  // Check date is valid
  
          $this->jd = $djm0 + $djm;  // Only set JD, keep day frac to save time
          return $this;
      }
docs: Sets the date for this instance
  
  @param  int $year  Year
  @param  int $month Month
  @param  int $day   Day
  
  @return static