def _convert_coordinates_to_decimal_degrees(
            self):
        """
        *convert coordinates to decimal degrees*
        """
        self.log.info(
            'starting the ``_convert_coordinates_to_decimal_degrees`` method')

        converter = unit_conversion(
            log=self.log
        )

        # CONVERT ALL COORDINATES TO DECIMAL DEGREES
        if len(self.listOfCoordinates) and isinstance(self.listOfCoordinates[0], str):
            sources = []
            sources[:] = [s.split(" ") for s in self.listOfCoordinates]

        else:
            sources = self.listOfCoordinates
        self.listOfCoordinates = []

        # TEST IF CONVERSION IS REQUIRED
        try:
            ra = float(sources[0][0])
            convert = False
        except:
            convert = True

        if convert == True:
            raDegs = []
            raDegs[:] = [converter.ra_sexegesimal_to_decimal(
                ra=s[0]) for s in sources]
            decDegs = []
            decDegs[:] = [converter.dec_sexegesimal_to_decimal(
                dec=s[1]) for s in sources]
            self.listOfCoordinates = []
            self.listOfCoordinates[:] = [[raDeg, decDeg]
                                         for raDeg, decDeg in zip(raDegs, decDegs)]

        else:
            self.listOfCoordinates = []
            self.listOfCoordinates[:] = [[float(s[0]), float(s[1])]
                                         for s in sources]

        self.log.info(
            'completed the ``_convert_coordinates_to_decimal_degrees`` method')
        return None
*convert coordinates to decimal degrees*