code: public function toMJD($scale = null)
      {
          $mjd = static::MJD;
  
          if ($scale) {
              return bcsub(bcadd($this->jd, $this->dayFrac, $scale), $mjd,
                $scale);
          } else {
              return $this->jd + $this->dayFrac - $mjd;
          }
      }
docs: Returns a Modified Julian date representation of this instance.
  
  @param  int $scale Optional additional decimal precision
  
  @return float|string