Mean vs True Lunar Nodes: Rahu and Ketu Settings
Compare mean and true lunar-node conventions, preserve the opposite-node relationship and investigate sign-boundary differences between Vedic charts.
Overview
Mean and true lunar nodes are different calculation models for the intersections of the Moon’s orbital plane with the ecliptic. Rahu and Ketu refer to the ascending and descending nodes in this chart vocabulary; they are not two additional physical planets.
At a glance
- Rahu
- Ascending lunar node
- Ketu
- Descending lunar node
- Model setting
- Mean node or true/osculating node
- Paired check
- The opposite node is 180° away within the same convention
The label true does not mean a true prediction
A mean-node model smooths the nodal motion; the true-node option represents a more instantaneous orbital construction. Swiss Ephemeris exposes separate body identifiers for them. The choice is an astronomical modeling convention, not an endorsement of a reading.
Do not compare a mean Rahu from one report with a true Ketu from another and expect the pair to be exactly opposite. First align the node setting, zodiac, time and coordinate flags.
A boundary example without a real birth claim
Imagine one model returning Rahu at 29°55′ and the other at 30°05′. The first falls in Aries, the second in Taurus. Their matching opposite nodes are 209°55′ and 210°05′, falling in Libra and Scorpio respectively.
These invented values illustrate a possible type of discrepancy, not its size on any particular date. If only Rahu and Ketu disagree while the physical bodies align, checking the node model is a focused first diagnostic step.
Which node should a reader use?
Use the convention specified by the method being reproduced and record it with the chart. Switching conventions to obtain a preferred interpretation destroys the consistency of the comparison.
A node near a sign, nakshatra or pada boundary deserves an unrounded position check. Do not infer a different fate from a rounded display. For a claimed software mismatch, provide the settings and numeric pair rather than only the two sign labels.
Sources and editorial basis
- P. V. R. Narasimha Rao: Vedic Astrology — An Integrated ApproachRao §§1.3.1–1.3.3, printed pp. 5–8: graha, longitude, sign and house vocabulary only. Numerical software settings and civil-time rules are supported separately by Swiss Ephemeris and IANA; the editorial checklists are not attributed to Rao.A named practitioner’s introduction to Jyotish. Used for terminology and a stated method, not universal school agreement or scientific validation. The added March 18, 2010 note describes changed views; it does not establish a fully revised 2010 edition.
- OpenFate Editorial MethodologyOpenFate Editorial Methodology, stable sections #editorial-principles, #editorial-workflow, #editorial-ai, and #editorial-context. Used for the calculation/interpretation and evidence-boundary policy.OpenFate separates deterministic chart calculation, traditional interpretation, and modern editorial explanation.
- Swiss Ephemeris Programmer’s Manual: Time, Sidereal Modes and HousesSwiss Ephemeris Programmer’s Manual §§3.2 and 3.4: separate mean/true lunar-node identifiers and position outputs. Supports the model distinction; the boundary values are synthetic.Primary software documentation for numerical time and position calculations. Sidereal modes, including named Lahiri variants, are explicit settings. The manual does not validate astrological interpretations.
- IANA Time Zone DatabaseIANA tz database theory.html, “Scope of the tz database” and “Accuracy of the tz database”; historical limitations, especially before 1970. This source does not verify an individual birth record.The maintained source for current and historical civil-time offsets and daylight-saving transitions; it provides timekeeping facts, not astrological interpretation.