Mean Lilith vs True Lilith: Which Black Moon Does Your Chart Show?

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Calculator note: Astrologist.com does not currently calculate Lilith placements. It has also not chosen between the conventions described here. This article is educational; it explains what the different labels mean so you can tell which Lilith another chart source is showing you.

If two astrology apps give you two different Lilith signs, neither is necessarily wrong. Black Moon Lilith is the Moon's apogee, the far end of its orbit, and there is more than one reasonable way to say where that point is at a given moment. Each method is a calculation convention. The name "True Lilith" sounds like a verdict on the others, but it is only a name.

Mean Lilith

Mean Lilith is the averaged apogee. It ignores the short-term wobbles in the Moon's orbit and follows the steady long-term turning of the orbit's axis. That makes it smooth and predictable. It always moves forward through the zodiac, slowly: NASA puts the turning of the axis at about 40.7 degrees a year, one full circle in about 8.85 years relative to the stars. On average that is roughly nine months per sign.

The Swiss Ephemeris, a widely used astronomical library, labels this point "Mean Lunar Apogee (Lilith, Black Moon in astrology)". Its documentation explains that it is derived from an analytical lunar theory and then projected onto the ecliptic, because the averaged orbit is tilted about five degrees to it.

Chart sources label it in different ways. A plain "Lilith" with no further label is not enough to know which convention you have; check the source's help pages or settings before relying on it.

True or Osculating Lilith

The osculating apogee is calculated differently. It takes the Moon's position and speed at one instant, works out the ellipse that would fit that motion if only the Earth and Moon existed, and reports the far end of that ellipse. Astrologers often call the result True Lilith. The Swiss Ephemeris labels it "Osculating Apogee (astrological True Lilith or True Dark Moon)".

The difficulty is that the Moon's orbit is heavily disturbed by the Sun's gravity. The fitted ellipse changes shape quickly, so the osculating apogee swings back and forth around the mean position over about a month. The Swiss Ephemeris documentation gives that swing as up to about 30 degrees either side of the mean point, and calls the oscillation largely an artifact of treating the Moon's orbit as a two-body problem. By its account, the Moon's actual monthly apogees never stray more than about five degrees from the mean position.

So "True" here means "calculated from the instantaneous orbit", not "more accurate as astrology" and not "the place where the Moon really reached its farthest point". The osculating point moves fast at times, can stop and turn back. The Swiss Ephemeris notes that it matches the Moon's real extremes only twice a month: when the Moon is at its farthest point and when it is at its closest.

A third option: interpolated or natural apogee

Because of that problem, some programs offer a third version. The idea behind it is to follow the Moon's real passages through apogee rather than a fitted ellipse. The Swiss Ephemeris documentation (section 2.2.4) adds that conventional interpolation did not work well for the lunar apsides, so the method it implements is derived from analytical lunar theory instead. Dieter Koch, one of the Swiss Ephemeris authors, called it the "interpolated" apogee; Juan Revilla preferred "natural", and according to the Swiss Ephemeris documentation Koch now prefers that name too. It stays within about five degrees of the mean position.

If your source offers a setting called interpolated, natural or realistic Lilith, this is what it means. It is less common than Mean or Osculating.

How far apart they get

The swings are big enough that the sign can differ for many birth dates. Two examples from the Swiss Ephemeris test page at Astrodienst (default compressed DE441 ephemeris, Tropical, geocentric, positions rounded to the minute):

In the first case all three agree on the sign. In the second, the osculating point is 22 degrees from the mean and crosses into Sagittarius during 3 January, while the mean moves just seven minutes of arc in the whole day. How to find your Lilith sign shows how these numbers were obtained and how to check your own date.

Do not confuse these with other "Liliths"

Asteroid 1181 Lilith is a main-belt asteroid discovered on 11 February 1927 by B. Jekhovsky at Algiers, according to NASA JPL's Small-Body Database. It is a physical object with its own orbit around the Sun and has nothing to do with the Moon's apogee.

The Dark Moon or Waldemath Moon is a supposed second moon of the Earth, described by a Dr Waldemath in 1898. The Swiss Ephemeris documentation notes that it has never been confirmed, even though an object of the claimed size should have been easy to find. Some astrologers still use positions computed for it. That hypothetical object is separate from Black Moon Lilith. Other authors use "Dark Moon" as a name for the lunar apogee, and in that case it may simply mean Black Moon Lilith; you still need to check which convention, Mean, Osculating or interpolated, the source used.

How this compares with Mean Node vs True Node

The Lunar Nodes have a similar split, explained in Mean Node vs True Node. The parallel is loose. The two Node conventions usually stay within a degree or two of each other. The two Lilith conventions can be tens of degrees apart, because an ellipse fitted to the Moon's disturbed motion is a much rougher model than the crossing line of two orbital planes. Astrologist.com has chosen the Mean Node for its charts; it has made no equivalent choice for Lilith.

Which one should you use?

There is no site-wide answer here. If you already work with one convention and it makes sense to you, keep using it and always say which one it is. If you are starting out, pick one before you read any interpretations, so you are not tempted to choose whichever sign sounds better.

When your Mean and Osculating Lilith fall in different signs, you can read both sign pages, clearly labelled, and compare. Keep them as two separate readings from two conventions rather than blending them into one placement. Noticing which description seems closer is a personal reflection, not evidence that one convention is right.

The meaning of the point itself is covered in Black Moon Lilith in astrology. For the placements Astrologist.com does calculate, use the free birth chart.

Related articles

• Black Moon Lilith in Astrology
• How to Find Your Lilith Sign
• Lilith in Cancer, Scorpio or Pisces
• Lilith in Aries, Leo or Sagittarius