Mean versus true lunar node
The declared node convention behind Rahu and Ketu and why node placements differ across software.
Calculation contract · released 2026-08-18
Definition
The mean node follows a smoothed precessing orbit-plane model; the true node adds periodic oscillation from the instantaneous lunar orbit model.
Calculation procedure
Select a node model, compute the ascending node in the declared frame, define the descending node as its antipode if that is the method, and label both explicitly.
Required inputs
- Instant and timescale
- Mean or true node model
- Reference frame
- Ketu/opposition policy
Maha convention
Maha natal charts use a Meeus mean-node polynomial for Rahu and define Ketu exactly 180° opposite.
Uncertainty and edge cases
Mean and true node longitudes can fall on different sides of sign, house, nakṣatra, or aspect boundaries.
What this does not establish
Neither node model has demonstrated predictive superiority in Maha’s current evidence corpus.
Authoritative references
These sources establish the calculation vocabulary, data product, or transformation convention. They do not establish astrological interpretation.
- Swiss Ephemeris general documentation
Astrodienst AG · 2.10 documentation, checked 2026-08-18
An independent ephemeris implementation, supported reference choices, house calculations, and its dual-license boundary.
Boundary: Maha does not bundle or call Swiss Ephemeris in production. Frozen conformance results are validation evidence, not permission to redistribute its software or data.
- Standards of Fundamental Astronomy
International Astronomical Union SOFA Board · 2023-10-11
IAU-approved algorithms for astrometry, time scales, Earth rotation, precession, nutation, coordinate transformations, and related fundamental astronomy.
Boundary: SOFA supplies standard algorithms and validation programs; an implementation must still record its exact release and input data products.