code: def get_coord_system_name(header):
      try:
          ctype = header['CTYPE1'].strip().upper()
      except KeyError:
          try:
              ra = header['RA']
              try:
                  equinox = float(header['EQUINOX'])
                  if equinox < 1984.0:
                      radecsys = 'FK4'
                  else:
                      radecsys = 'FK5'
              except KeyError:
                  radecsys = 'ICRS'
              return radecsys.lower()
          except KeyError:
              return 'raw'
      match = re.match(r'^GLON\-.*$', ctype)
      if match:
          return 'galactic'
      match = re.match(r'^ELON\-.*$', ctype)
      if match:
          return 'ecliptic'
      match = re.match(r'^RA\-\-\-.*$', ctype)
      if match:
          hdkey = 'RADECSYS'
          try:
              radecsys = header[hdkey]
          except KeyError:
              try:
                  hdkey = 'RADESYS'
                  radecsys = header[hdkey]
              except KeyError:
                  try:
                      equinox = float(header['EQUINOX'])
                      if equinox < 1984.0:
                          radecsys = 'FK4'
                      else:
                          radecsys = 'FK5'
                  except KeyError:
                      radecsys = 'ICRS'
          radecsys = radecsys.strip()
          return radecsys.lower()
      match = re.match(r'^HPLN\-.*$', ctype)
      if match:
          return 'helioprojective'
      match = re.match(r'^HGLT\-.*$', ctype)
      if match:
          return 'heliographicstonyhurst'
      match = re.match(r'^PIXEL$', ctype)
      if match:
          return 'pixel'
      match = re.match(r'^LINEAR$', ctype)
      if match:
          return 'pixel'
      return 'icrs'