the
            correction applied to the position of the distant
            object. For example, if a star position is obtained from
            a catalog, the position vector may not be corrected for
            stellar aberration. In this case, to find the angular
            separation of the star and the limb of a planet, the
            vector from the observer to the planet should be
            corrected for light time but not stellar aberration.


      4) Obtain an uncorrected position vector der