Synastry keeps two charts distinct
Synastry compares the planetary positions in person A's chart with those in person B's. A biwheel can place one set inside and the other outside, while an inter-aspect table names measured separations and orbs. If one Venus lies at 10° Aries and the other Mars at 12° Leo, their shorter separation is 122°, within 2° of a trine. The geometry does not prove compatibility or predict a relationship outcome. Each natal chart remains its own record, so a reading should keep the two people distinguishable and avoid treating a single aspect as a verdict.
A midpoint composite is a derived chart
A composite takes the midpoint of corresponding natal positions: Sun with Sun, Moon with Moon, and so on. It produces one set of derived longitudes, not a sky photographed at an actual moment. Points nearly opposite one another need a declared midpoint convention because a circle offers two opposing halfway directions. House and angle methods can also differ between calculators. A reader should see the method in the result header and compare like with like before interpreting a mismatch. A composite is a lens on a relationship, not a substitute for either person's chart.
Davison uses a midpoint event
A Davison relationship chart instead finds a midpoint of the two birth instants and a chosen geographic midpoint, then calculates a chart for that derived time and place. Unlike the planetary midpoint composite, its planet positions come from an ephemeris at one actual instant. Its geographic midpoint convention needs to be stated; a flat average of longitude can fail across the date line. The resulting angles and houses require both birth times and coordinates. Its result should be distinguished from a planetary midpoint composite.
Uncertainty and ethical use
If either birth hour is unknown, sign and interplanetary comparisons may still be possible, but angles and houses should be withheld or clearly qualified. Historical time-zone errors propagate into both records. The final reading should describe which points were compared, the allowed orb, and the source quality of both records. No chart can establish consent, character, or the future of a relationship.
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Updated 20 September 2026