code: def to_julian_date(self):
          
  
          # http://mysite.verizon.net/aesir_research/date/jdalg2.htm
          year = np.asarray(self.year)
          month = np.asarray(self.month)
          day = np.asarray(self.day)
          testarr = month < 3
          year[testarr] -= 1
          month[testarr] += 12
          return (day +
                  np.fix((153 * month - 457) / 5) +
                  365 * year +
                  np.floor(year / 4) -
                  np.floor(year / 100) +
                  np.floor(year / 400) +
                  1721118.5 +
                  (self.hour +
                   self.minute / 60.0 +
                   self.second / 3600.0 +
                   self.microsecond / 3600.0 / 1e+6 +
                   self.nanosecond / 3600.0 / 1e+9
                   ) / 24.0)
docs: Convert Datetime Array to float64 ndarray of Julian Dates.
          0 Julian date is noon January 1, 4713 BC.
          http://en.wikipedia.org/wiki/Julian_day