*Convert an RA, DEC coordinate set to x, y, z cartesian coordinates*

        **Key Arguments:**
            - ``ra`` -- right ascension in sexegesimal or decimal degress.
            - ``dec`` -- declination in sexegesimal or decimal degress.

        **Return:**
            - ``cartesians`` -- tuple of (x, y, z) coordinates

        ..  todo::

            - replace calculate_cartesians in all code

        **Usage:**

            .. code-block:: python 

                from astrocalc.coords import unit_conversion
                converter = unit_conversion(
                    log=log
                )
                x, y, z = converter.ra_dec_to_cartesian(
                    ra="23 45 21.23232",
                    dec="+01:58:5.45341"
                )
                print x, y, z

                # OUTPUT: 0.9973699780687104, -0.06382462462791459, 0.034344492110465606

def ra_dec_to_cartesian(
            self,
            ra,
            dec):
        """*Convert an RA, DEC coordinate set to x, y, z cartesian coordinates*

        **Key Arguments:**
            - ``ra`` -- right ascension in sexegesimal or decimal degress.
            - ``dec`` -- declination in sexegesimal or decimal degress.

        **Return:**
            - ``cartesians`` -- tuple of (x, y, z) coordinates

        ..  todo::

            - replace calculate_cartesians in all code

        **Usage:**

            .. code-block:: python 

                from astrocalc.coords import unit_conversion
                converter = unit_conversion(
                    log=log
                )
                x, y, z = converter.ra_dec_to_cartesian(
                    ra="23 45 21.23232",
                    dec="+01:58:5.45341"
                )
                print x, y, z

                # OUTPUT: 0.9973699780687104, -0.06382462462791459, 0.034344492110465606
        """
        self.log.info('starting the ``ra_dec_to_cartesian`` method')

        ra = self.ra_sexegesimal_to_decimal(
            ra=ra
        )
        dec = self.dec_sexegesimal_to_decimal(
            dec=dec
        )

        ra = math.radians(ra)
        dec = math.radians(dec)
        cos_dec = math.cos(dec)
        cx = math.cos(ra) * cos_dec
        cy = math.sin(ra) * cos_dec
        cz = math.sin(dec)

        cartesians = (cx, cy, cz)

        self.log.info('completed the ``ra_dec_to_cartesian`` method')
        return cartesians