Calculation research
True vs. Mean Lilith & North Node: Degree Differences Explained
By Natal Chart Lab ·
Mean and true lunar points use different mathematical definitions. They can give different degrees even with identical birth data. In the example for October 27, 2026, at 00:00 UTC, mean Black Moon Lilith is 4°43′ Capricorn, while osculating (“true”) Lilith is 12°45′ Sagittarius: a signed difference of -21.965° and a different sign.
Our Lilith calculator and North Node calculator use mean points. They do not currently offer a true/mean switch. The comparison below uses Swiss Ephemeris for both sides, isolating the definition change within one engine.
Mean vs. osculating Black Moon Lilith
Mean Lilith follows a smoothed lunar apogee. Osculating Lilith derives an instantaneous ellipse from the Moon’s position and velocity. The Moon’s perturbed orbit is not a fixed two-body ellipse, so “true” is a conventional name, not a promise that it is the uniquely correct choice. An interpolated or natural apogee is another definition. Black Moon Lilith is also distinct from asteroid 1181 Lilith.
| Date | Mean | Osculating | Signed difference |
|---|---|---|---|
| 2026-01-01 | 1°15′ Sagittarius | 22°03′ Sagittarius | +20.790° |
| 2026-04-01 | 11°20′ Sagittarius | 14°39′ Sagittarius | +3.306° |
| 2026-07-01 | 21°32′ Sagittarius | 25°37′ Sagittarius | +4.088° |
| 2026-07-03 | 21°45′ Sagittarius | 2°56′ Capricorn | +11.178° |
| 2026-10-27 | 4°43′ Capricorn | 12°45′ Sagittarius | -21.965° |
| 2026-11-01 | 5°17′ Capricorn | 5°56′ Sagittarius | -29.347° |
Mean vs. true North Node
The North Node is the ascending intersection of the lunar orbital plane and the ecliptic, not an apogee. The mean node smooths periodic variation; the true node follows an instantaneous orbital plane. Node differences are much smaller than the Lilith differences in these examples. Close to a 30° boundary, even a small degree difference can change the sign. Do not apply a Lilith correction to a node.
| Date | Mean | True | Signed difference |
|---|---|---|---|
| 2026-01-01 | 12°10′ Pisces | 10°57′ Pisces | -1.217° |
| 2026-04-01 | 7°24′ Pisces | 8°46′ Pisces | +1.361° |
| 2026-07-01 | 2°35′ Pisces | 0°52′ Pisces | -1.717° |
| 2026-07-03 | 2°29′ Pisces | 0°43′ Pisces | -1.764° |
| 2026-10-27 | 26°20′ Aquarius | 27°30′ Aquarius | +1.164° |
| 2026-11-01 | 26°04′ Aquarius | 26°56′ Aquarius | +0.863° |
Sources, reproducibility and limits
These examples use Swiss Ephemeris 2.10.03, pyswisseph 2.10.3.2, and the Moshier ephemeris flag (FLG_MOSEPH), with tropical geocentric ecliptic longitudes through calc_ut. We selected January 1, April 1, July 1 and October 27, plus the largest absolute difference for each point among 365 samples at midnight UTC in 2026. These are sampled maxima, not continuous extrema or all-time records. Differences are wrapped into [−180°, 180°); degree labels are rounded separately from the differences.
Download the full-precision examples (JSON) · Reproduce the examples (Python) · Swiss Ephemeris definitions and precision. Install the pinned pyswisseph version named in the script before running it.
The site’s calculators use Meeus mean-point polynomials; the reference examples use Swiss Ephemeris mean-point conventions. They need not agree in every arcminute. These tables compare definitions, not certify agreement between every implementation. If two websites disagree, first align the UTC time, tropical versus sidereal zodiac, point definition and coordinate conventions. See our calculator comparison checklist.
Prepared with AI assistance and checked against calculation code and saved data. Tables state their definitions and limits; astrological interpretations are not established by these calculations.