The Davison relationship chart
Ronald C. Davison, Synastry: Understanding Human Relations Through Astrology, New York, 1977
Ronald Davison sat at the centre of British astrology for a generation, editing the Astrological Journal and presiding over the Astrological Lodge of London. His relationship chart takes a different route from the composite: instead of averaging the planets, it averages the two births themselves — the midpoint in time and the midpoint in space — and then casts an ordinary chart for that moment and place. He called it the relationship horoscope; the name “Davison chart” is the community's.
What it measures
A real chart of a real instant at a real location, both of which happen to lie halfway between two births. Because it is an ordinary chart, it has everything a chart has: true planetary speeds, retrogrades, and houses that were actually rising there. That is the whole argument for it over the composite.
Where practitioners disagree
- How is the midpoint in space taken?
The great-circle midpoint on the sphere — or a naive average of the latitude and longitude figures
The two diverge badly for distant births; the naive average is not a point on the shortest path between them.
This engine: The great-circle midpoint.
Sources
- Ronald C. Davison, Synastry: Understanding Human Relations Through Astrology (1977)