Orbit of the secondary around the primary, which is approximately at the point (0,0). The coordinate units are given in AU. The disk is seen edge-on. The secondary orbits the primary in a counter-clockwise sense. The last point in the orbit is in the year 1915; the previous disk crossings occurred in 1912 and 1910. The disk crossing farthest to the left happened in 1903, and previous crossings were in 1898 and 1895. Because of precession the intervals between disk crossings vary greatly.