Definition
The descending node (☋) is where the orbit crosses the reference plane with ecliptic latitude decreasing. Eclipses can only occur near the nodes when the Sun is close to the node line.
Descending Node
Where an orbit crosses the reference plane moving southward.
3D illustration
The descending node complements the ascending node on every orbit.
Use the menu and time controls to explore. Based on Jean Meeus' Astronomical Algorithms.