The lunar nodes are the orbital nodes of the Moon, that is, the points where the orbit of the Moon crosses the ecliptic (which is the apparent path of the Sun across the heavens against the background stars). The North (or Ascending) Node is where the Moon crosses to the North of the ecliptic; the South (or Descending) Node where it crosses to the South.
The lunar nodes are the only points on the Moon's orbit where eclipses occur. Solar eclipses occur when the passage of the Moon through a node coincides with the New Moon; lunar eclipses occur when it coincides with the Full Moon. The lunar nodes precess rather quickly around the ecliptic, completing a revolution (called a draconitic or nodical period) in 6793.5 d or 18.5996 a.
If one tracks the Moon in the sky on a continuous basis, one will notice its declination (celestial latitude) oscillates regularly between extreme values. Every half-synodical month (about 27 times per year), the Moon reaches a maximum of minimum declination value. This is called a standstill (the word has the same meaning as the "-stice" part of "solstice").
Because the Moon's orbit maintains a relatively constant inclination with respect to the ecliptic but precesses rather quickly about the ecliptic pole (completing a cycle in a little less than 19 years), the declination it can reach in the sky varies accordingly between limits of about 28.59° and 18.29°. This affects strongly the azimuth of moonrise and moonset. If an observer tracks the position on his horizon of successive moonrises, for example, it will appear to travel north, reach some maximum value, then travel south, reach a minimum value, and then head north again, over a period of nearly 19 years. When the Moon is nearing its maximum declination or moonrise/set azimuth, it will appear to rise or set in the same spot several nights in a row —this is the major standstill. When the Moon nears the minimum declination or moonrise/set azimuth, the same phenomenon occurs, and is dubbed the minor standstill. Prehistoric astronomers knew about this phenomenon and kept track of it.
The Lunar Nodes in Astrology
Another symbol shown on the natal chart/horoscope is that of the North Lunar Node. This symbol looks like a horseshoe, although it represents the constellation [Draco]. The only difference in the symbol is that the horseshoe is open on the bottom for the North Node (☊) and open on the top for the South Node (☋). The Lunar Nodes, north and south, are not planets or physical in any way; they are purely geometric.
When the Sun and Moon are in conjunction, and either lunar node is also in conjunction with both, a solar eclipse occurs. When the Sun and Moon are in opposition, and each is in conjunction with one of the lunar nodes, a lunar eclipse occurs.
The North Lunar Node is called by a couple of other names in different areas of the World. Since it is the point at which the interception is made while the Moon is ascending from the south to the north, it is also called the Ascending Node. From Hindu astrology (or Jyotish), the term Dragon's Head (Caput Draconis) is used for the North Node. The South Lunar Node is also known as the Descending Node or the Dragon's Tail (Cauda Draconis).
The lunar nodes are of major significance in Vedic astrology, and are considered to a limited degree in Western astrology. Usually only the North Node is marked in natal charts, as the South Node is by definition always exactly 180° removed, that is, it is located at the exact opposite point in the astrological chart.
Delineation techniques of the lunar nodes vary widely. In general, however, the North Node is viewed a point of opportunity for growth and development and self help, while the South Node is thought to represent karmic repression or tendencies that restrict growth. The North Node carries the positive and ultra-beneficial tone of Jupiter, while the South Node expresses the restrictions and obstacles of Saturn. Another thought on this is that the North Node represents positive objectives and the South Node denotes the easy way out with little opportunity for growth. In many schools of astrology, the nodes are thought to reflect an individual's karma or spiritual past. The two nodes together are often referred to simply as the nodal axis.