The South Node, or descending node, is the point opposite the North Node, where the Moon crosses the ecliptic going south. Western tradition called it the Dragon's Tail, cauda draconis, and read it as decreasing, in the same way that the Head was read as increasing; the pair were treated as a modifying influence on whatever they contacted rather than as bodies with independent significations. In Indian astrology the South Node is Ketu, the severed body of the same demon, and it is read for detachment, loss, spiritual liberation and the results of past action, and is a full participant in the dasha systems by which Indian astrology times events. The modern western reading of the nodal axis as past and future lives, with the South Node as inherited habit and the North Node as the direction of growth, is a twentieth-century development, drawing on theosophical ideas of reincarnation, and is not found in the classical or medieval sources.
The node also carries the two periods that make it usable for timing. It regresses through the whole zodiac in about 18.6 years, so the nodal return falls at about nineteen, thirty seven and fifty six, and the nodal reversal, when the axis is exactly opposite its natal place, falls midway between. In the Indian scheme those figures are formalised: the Vimshottari dasha system allots Ketu 7 years and Rahu 18 out of a total cycle of 120, and both are handled exactly as the seven grahas are, with sub-periods and their own significations. The western tradition, having read the nodes as modifiers rather than as agents, developed no comparable timing use for them.