How does an ascending node identify where an orbit crosses a reference plane?

In celestial mechanics, an orbit is a path defined by an inclined plane that intersects a reference plane, such as the ecliptic (the plane of Earth's orbit around the Sun). The points where these two planes intersect are known as nodes.12

The ascending node specifically identifies the point in the orbit where a celestial body crosses from the south side of the reference plane to the north side. Conversely, the descending node is the point where the body crosses from the north to the south side.12

These nodes are fundamental to defining the orbital elements of a body, as the longitude of the ascending node is one of the key parameters used to fix the orientation of the orbit plane in space. Because of gravitational perturbations—such as the influence of the Sun on the Moon or the equatorial bulge of Earth on artificial satellites—the position of these nodes can shift or regress over time.23