docs: def __to_format(jd: float, fmt: str) -> float:
      """
      Converts a Julian Day object into a specific format.  For
      example, Modified Julian Day.
      Parameters
      ----------
      jd: float
      fmt: str
  
      Returns
      -------
      jd: float
      """
      if fmt.lower() == 'jd':
          return jd
      elif fmt.lower() == 'mjd':
          return jd - 2400000.5
      elif fmt.lower() == 'rjd':
          return jd - 2400000
      else:
          raise ValueError('Invalid Format')