As I understand it from Astronomical Algorithms, by Jean Meeus, the Longitude of Perihelion is a very common numeric value associated with planets, even used as one of the planetary orbital elements. As I understand it, the Long.ofPeri is the sum of the Argument of Perihelion and the Longitude of the Ascending Node.
Here is my dilemma. The Long.ofAsc.Node is an angle measured from within the Ecliptic. The Arg.ofPeri is an angle measured in the associated planets orbital plane. These planes are separated by the Inclination between them, as they intersect only at the line of nodes.
Im a mathematician, primarily. I dont understand the basis of this measure, the Long.ofPeri. This seems invalid to me. It may be used, but perhaps this is where some inaccuracy comes from in your predictions? Why use it at all if its invalid?
From mathematics/geometry, we learn that you CANNOT add two angles in the sort of way that we are apparently doing here. These two angles are in different planes. They are not parallel, and at their point of adjacency they split off in entirely different directions.
I prefer to use the Arg.ofPeri and the Long.ofAscNode separately. Conceptually it makes sense and the mathematics Im more certain about.