The nodes are mathematical points that represent where the orbit of the Moon around the Earth crosses the ecliptic (which is the apparent path of the Sun around the Earth). The North Node and the South Node are always exactly opposite each other in the chart.
Readers, please enjoy this guest blog post by Sandra Kynes, author of several books, including The Herb Gardener's Essential Guide, Plant Magic, and the new Witches' Encyclopedia of Magical Plants, among many others.
Although a few old books...