descending node

In astronomy, a node is a point where the orbital plane of a celestial body, like the Moon or a planet, intersects with the plane of the ecliptic. The ecliptic is the apparent path of the Sun across the celestial sphere.

The descending node is specifically the point where a celestial body crosses from the north side to the south side of the ecliptic. Conversely, the ascending node is where it crosses from south to north. Eclipses of the Sun or Moon can only happen when the Moon is near one of these nodes. Similarly, transits of inner planets across the Sun occur when these planets are near a node.1