A node is one of two points where a body's orbit crosses the ecliptic, called the ascending node (when the body is moving northward) and descending node (when the body is moving southward). The lunar nodes are subject to lunar precession, this is the gradually shift westward because of the gravitational pull of the Sun upon the Moon. (See also: eclipse)
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 lunar nodes precess rather quickly around the ecliptic, completing a revolution (called a draconitic or nodical period, the period of nutation) in 6793.5 days or 18.5996 years (please beware that this is not the saros eclipse cycle).
Since the ascending node is the point of intersection between the ecliptic and the plane of the lunar orbit where the Moon is ascending from the South to the North, it is sometimes called the North node.
The lunar nodes are the points where the moon's line of nodes, when extended, strike the celestial sphere.
The lunar nodes regress (move westward along the ecliptic) due to perturbations from the other bodies in the solar system, e.g., the sun and planets.
The ascending node, when the sun appears to cross the celestial equator from south to north, is the vernal equinox; the descending node is the autumnal equinox.
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