Node
every reader
What the tradition reads
The lunar nodes are the two points where the Moon's orbit crosses the ecliptic, the Sun's own apparent path: the north or ascending node marks where the Moon moves into the northern ecliptic hemisphere, and the south or descending node, always exactly opposite it, marks where it enters the southern hemisphere. Both points matter because an eclipse can only occur when a new or full Moon falls near one of them, the crossing itself being the intersection that makes the alignment of Sun, Earth and Moon possible at all; a lunar eclipse can occur within about eleven and a half degrees of a node and a solar eclipse within about seventeen and a half degrees, which is why eclipses cluster into a season around each crossing rather than falling at any point in the month. Vedic astrology treats the nodes as full grahas in their own right, Rahu at the north node and Ketu at the south, shadow planets with no physical body and no sign of their own to rule; despite having no physical existence, Rahu is counted, with the seven classical planets, among the nine navagrahas, allocated the standing of a full planet for the strength of its influence. The daily period Rahu is held to rule, Rahu kala, is treated in Vedic practice as an inauspicious stretch of time in which to avoid starting anything important.
The story
The image of a dragon behind the nodes is medieval rather than ancient: Arabic astronomers of the early medieval period named an eighth, invisible body al-Tinnin, the Dragon, believed to be the cause of solar and lunar eclipses, and split its single body into a Head, ra's, and a Tail, dhanab, matching the two points where the Moon's path crosses the ecliptic. Latin astrology translated these directly as caput draconis and cauda draconis, the head and tail of the dragon, terms and their symbols that persisted in Western astrological manuals long after the underlying mechanism of eclipses was properly understood as ordinary orbital geometry rather than any creature's appetite. Vedic astrology arrived at an equivalent two part, head and tail structure by its own route, naming the ascending node Rahu and the descending node Ketu among the nine navagrahas, and its own account of Rahu, cast as a serpent, gives the eclipse its more vivid image: Wikipedia's own page on Rahu records that the Sun or Moon coinciding with these very crossing points gave rise to the understanding of the Sun and Moon being swallowed by that snake. Two quite separate traditions, working from different mythic material, converged on the same underlying image of the node as a devouring, bisected body rather than a single ordinary point.
Written from
Corpus key glossary:node.