Davison Chart: The Time-Space Midpoint Method
Imagine two people born years apart in different cities, and then ask what the sky looked like at the exact halfway point between those two births, in time and in place. That is a Davison chart. It is cast for a moment that actually occurred, at a location on the map, so it behaves like any other chart: planets in their true positions, a real Ascendant, houses drawn from a real horizon. The method was set out by Ronald Davison in 1977, and it is the main alternative to the composite chart, which averages planet positions instead. One way to see its appeal is the plain fact that it describes a real sky.
Halfway through time
The first step is to find the midpoint between two birth moments. Convert each birth date and time to a common standard so time zones do not distort the sum, then take the point exactly halfway between them. If one person was born in the evening of one day and the other the following morning, the midpoint falls overnight between them. If the births are decades apart, the midpoint falls somewhere in the years between, down to the hour and minute. The result is a single date and clock time that is real, because the sky had a definite state at that instant. It always falls between the two births, never outside them, and a pair born closer together gets a midpoint closer to both.
Halfway across the map
The second step does the same for place. Take the latitude and longitude of each birthplace and find the halfway point between the two locations. That point may be a town, a field or open water, and it need not be anywhere either person has visited. Together with the midpoint in time, it gives the method its other name, the time-space midpoint. Placing the chart on the map is what supplies an Ascendant and houses, which a purely arithmetic chart cannot give without a construction rule.
Ronald Davison and the 1977 book
Ronald Davison described this relationship chart in his 1977 book Synastry. The method sits in the same family as the composite chart but differs in how it handles the midpoint. The method finds the midpoint of the moments themselves and lets the sky supply the positions, instead of averaging the planets after the fact.
A real sky against averaged planets
The composite chart averages planet positions, so it describes a configuration that no sky ever showed. The Davison chart averages the moment and place, so every planet stands where it truly stood at that midpoint. The two methods can therefore give different pictures of the same pair. A composite Sun is the halfway point of two Suns. A Davison Sun is wherever the Sun actually was on the midpoint date. Each fits a different idea of what a relationship chart should be: one is a blend of two charts, the other is a chart of its own. Because the Davison planets are in true positions, the Moon's phase and any retrograde planet are simply those of the midpoint date, exactly as in a natal chart.
A chart of the pair's own character
Because it is a genuine chart, a Davison can be read with ordinary methods: planets in sign and house, aspects, the Ascendant and angles. What sets it apart is that its Ascendant, Midheaven and houses come from a real horizon at the midpoint place, so house placements are read as they would be in any natal chart, without the construction rule a composite needs. The planets stand where the sky put them at the midpoint moment, so aspects between them are true angles. Reading it as the chart of the pair's own character is an interpretation, and astrologers differ on how much weight it deserves next to synastry and the composite.
Where the method gets awkward
The Davison depends on exact birth times and places for both people, so a missing or uncertain birth time makes the midpoint uncertain. Very distant birthplaces can put the midpoint in an unusual location, such as the middle of an ocean, which is fine for a sky calculation but strange to talk about. Both facts are worth knowing before leaning on the result, and so is the fact that different programs may find the halfway point between two locations in slightly different ways. Treat the chart as one more perspective on the relationship, to be set beside the natal charts and the aspects between them, not as the last word.
A Davison chart corresponds to an actual moment and place: you could, in principle, have stood there and looked up.
How synastry compares two birth charts — read the guide →
Get your personal AI birth chart reading — create a free account →
Frequently Asked Questions
Why is the midpoint of place needed as well as the midpoint of time?
The midpoint of time gives the date and clock time, and so the planets' positions. The midpoint of place, found from the latitude and longitude of both birthplaces, supplies the horizon, so the chart has an Ascendant, a Midheaven and houses. Without both, you would have a sky but no angles. Chart software finds both from two sets of birth data.
What sets a Davison apart from a composite chart?
The Davison takes the midpoint of time and place, so its planets sit where they truly were at that moment. The composite takes the midpoint of each pair of planets directly, giving positions no sky ever showed. The Davison is a real chart; the composite is a calculation. Both are used to describe a relationship.
Where does synastry end and the Davison chart begin?
Synastry compares two separate charts by reading aspects between one person's planets and the other's. The Davison merges the two births into a single chart cast for one midpoint in time and space. Ronald Davison described the method in his 1977 book Synastry.
Can you use a Davison chart without a birth time?
It becomes less reliable, because the midpoint in time depends on both birth times. Without them the Ascendant and houses cannot be set with confidence, and the Moon's position shifts across the day. You can still compute a chart for a chosen time, such as noon, but treat the angles and houses as uncertain, and lean on planets and aspects.