106 Ebertin midpoints
Western · Esoteric
Reinhold Ebertin's Cosmobiology — the system underlying the 106 midpoints — is a streamlined, sign-free branch of Western astrology that analyses the precise halfway point between every pair of planets as a sensitive point in the chart, activated when a third planet, transit, or progression lands there.
What it is
Cosmobiology was developed by Reinhold Ebertin (1901–1988) and systematised in his landmark work 'Combination of Stellar Influences' (Kombinationslehre der Gestirne, first published 1940). It is derived from the earlier work of Alfred Witte and the Hamburg School (Uranian astrology) but stripped of the hypothetical planets and simplified for clinical and psychological application.
The core concept: for every pair of planets A and B in a chart, the midpoint (A/B) is calculated as the arithmetic mean of their ecliptic longitudes. This midpoint is a 'sensitive degree' — neutral until activated by a third factor (a natal planet, a directed/progressed planet, a transit) within a very tight orb (0°–1.5° for exact, 2–3° for operational). When activated, the combination A/B = C describes a precise psychological or biographical theme expressed through the synthesis of all three planetary principles.
With 10 standard planets (Sun through Pluto) there are 45 distinct two-planet pairs, each producing a midpoint. Adding the Ascendant, MC, and sometimes Aries Point (0° Aries as a collective sensitive point) raises the total to over 100 combinations — hence the '106 midpoints' figure. Ebertin catalogued interpretations for each two-planet midpoint and the most significant three-planet combinations.
How it is calculated
Step 1: Calculate all planetary longitudes in the tropical zodiac. Step 2: For each pair of planets (A, B), compute the direct midpoint: (longitude_A + longitude_B) / 2. If the result is > 360°, subtract 360°. Also compute the indirect midpoint: add 180° to the direct midpoint (modulo 360°) — both are active sensitive points. Step 3: Build a midpoint sort — a list of all midpoints ordered by their degree position around the 360° zodiac. Step 4: Check which natal planets, Ascendant, or MC fall at or within 1.5° of any midpoint to find natal activations. Step 5: For timing, check which transiting or directed planets are within 1.5° of any midpoint.
Modern Cosmobiology works primarily with the 90° dial — a tool invented by Witte that compresses all 360° into a 90° view, so that 0°, 90°, 180°, and 270° positions all overlap. This makes the conjunction and square aspects (which Ebertin's system treats as equivalent since they share the same 90° family) clearly visible on one compact wheel.
What it reveals
Midpoint analysis reveals the specific psychological and biographical themes encoded in the interface zones between planetary pairs. The Sun/Moon midpoint (often called the 'soul point') describes the core psychophysical balance and is one of the most sensitive personal points in Cosmobiology. When Saturn activates the Sun/Moon midpoint by transit, it often coincides with periods of serious health or relationship restructuring. Venus activating Sun/Moon brings harmony and relationship happiness.
Ebertin's system excels at precise event timing. When multiple midpoints are simultaneously activated by a transit or solar arc direction, the combined interpretation of those midpoints (read from 'Combination of Stellar Influences') gives a remarkably specific description of the types of events likely to occur. This specificity — especially when combined with traditional aspect analysis — makes Cosmobiology one of the most powerful forecasting tools in the Western astrological toolkit, widely used by medical astrologers and researchers for its repeatable, testable nature.
Frequently asked questions
Do midpoints use the tropical or sidereal zodiac?
Ebertin's Cosmobiology uses the tropical zodiac exclusively. The system is also sign-free and house-free in its purest form — the 90° dial strips away sign boundaries, focusing purely on degree positions and angular relationships. This makes it compatible with any Western tropical chart without modification.
What orb is used for midpoint activation?
Ebertin recommended very tight orbs: 0°–1°30' for exact or 'hard' activation (conjunction, square, opposition), and up to 2°–3° as the operational boundary. This is much tighter than traditional aspect orbs. The tightness is intentional — the precision of the technique depends on working with high-confidence activations rather than broad possibility zones.
Is Cosmobiology compatible with traditional aspect-based chart reading?
Yes. Most modern astrologers using Cosmobiology combine it with traditional chart interpretation rather than replacing one with the other. Traditional aspects and house analysis establish the natal themes and character; midpoint analysis adds a layer of precise temporal activation and psychological nuance. The two approaches are complementary — Cosmobiology is especially valued for its power in event timing and psychological diagnosis.
Classical sources
- Ptolemy, Tetrabiblos
- William Lilly, Christian Astrology
Related techniques
See it in your chart
Generate your chart and let the AI read this technique in your own words.