← Encyclopedia of Astrology · lesson 223/235
Davison chart
What it is
The Davison chart, or Davison relationship chart, gives a relationship a chart of its own — like the composite chart — but builds it in a more concrete way. Instead of averaging two sets of planetary positions, it averages the births themselves: it finds the moment exactly halfway in time between the two birth moments, and the place halfway between the two birthplaces, and casts an ordinary chart for that moment and place.
It is named after the British astrologer Ronald C. Davison, who set the method out in his book Synastry (1977).
How it is worked out
- The midpoint in time. Both birth times are turned into Universal Time, and the instant halfway between them is found. Two people born ten years apart give a Davison moment five years after the first birth.
- The midpoint in space. The two birthplaces are averaged. Davison's own method averages the latitudes and the longitudes as numbers. Others take the true midpoint on the globe, along the great circle joining the two places, which behaves better when the places are far apart or straddle the date line. A few cast the chart for where the couple live instead.
- The chart. A normal chart is then cast for that moment and place, with houses drawn by the chosen house system.
There are variants. One "corrected" form keeps the averaged place but adjusts the time slightly so that the Davison Midheaven matches the composite Midheaven. Astrologers differ on which they trust.
Why it differs from a composite
The difference is not just technical. A composite is an elegant abstraction: an average of positions that may never have occurred together in any sky. A Davison is a real sky, one that actually stood over a real place at a real moment. So its planets keep their true relationships to one another — Mercury and Venus stay as close to the Sun as they really can — and it can be treated exactly like a birth chart: transits can be run to it and it can be progressed.
The two often agree on broad themes, because the slow planets average to much the same places either way, but the Moon, the angles and the houses can differ markedly.
How it is read
A Davison is read as the chart of the bond, much as a natal chart is read for a person: the Sun for what the relationship is about, the Moon for its emotional climate, the Ascendant for how it meets the world, the houses for the areas of life it tends to live through. It is usually read beside synastry, which shows the chemistry between the two people.
Like every relationship technique, it describes tendencies and themes, not the fate of a relationship.
In a reading here
Davison readings here find the midpoint of the two birth moments in Universal Time and the great-circle midpoint of the two birthplaces, and cast a full chart for them.