Davison Methodology

Interpretation/Charts/Davison/methodology.md

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Davison Methodology

1. Calculate the midpoint date and location.
2. Construct a new chart for that moment.
3. Interpret as a standard natal chart but for the relationship entity.

Backlink: Davison Overview.

🧮 Worked Arithmetic

1. Convert both births to UT and Julian Day: JD_A, JD_B.
2. JD_mid = (JD_A + JD_B) / 2 → convert back to a UT calendar date/time.
3. φ_mid = (φ_A + φ_B) / 2; L_mid = (L_A + L_B) / 2 (if the longitudes differ by more than 180°, add 360° to the smaller before averaging and normalise the result).
4. Cast an ordinary chart for JD_mid at (φ_mid, L_mid) in the vault’s house system.
5. Interpret as a natal chart of the relationship; then compare it to each partner’s natal chart.

Example (arithmetic only): JD_A = 2447892.5, JD_B = 2448622.5 → JD_mid = 2448257.5 (exactly 365 days after A).

Ronald C. Davison’s relationship chart (1977): a real chart cast for the midpoint in time and the midpoint in space between two births. Arithmetic: JD_mid = (JD_A + JD_B) / 2 (both in UT); φ_mid = (φ_A + φ_B) / 2; L_mid = (L_A + L_B) / 2, taking the shorter way around the globe (some programs use the great-circle midpoint instead). Because it is a real moment, the Davison chart has genuine planetary positions, houses and its own transits and progressions — unlike the composite (midpoint) chart.

Sources (method)

• Ronald C. Davison, Synastry: Understanding Human Relations Through Astrology (1977) — the Davison relationship chart (midpoint in time and space)
• Jean Meeus, Astronomical Algorithms, 2nd ed. (Willmann-Bell, 1998) — ch. 13 (coordinate transforms), ch. 47 (Moon, nodes, perigee/apogee)