Choose synastry when you want to know which point in one person’s chart contacts a point in another’s. Choose a midpoint composite when you want a single symbolic chart derived from both sets of positions. The difference begins with the calculation, before interpretation.
| Question | Synastry | Midpoint composite |
|---|---|---|
| What is drawn? | Two distinct natal charts and contacts between them. | One derived set of matching planetary midpoints. |
| Can I tell whose planet it is? | Yes. Each point retains its chart owner. | No. Both birth charts contribute to each midpoint. |
| Unknown birth hour? | Many planetary comparisons remain possible; Moon and angles need caution. | Planetary midpoints may be explored with caveats; angles and houses need reliable times. |
| What does an aspect join? | One point from each natal chart. | Two derived composite points. |
When the charts seem to disagree
Suppose a pair has a close Venus–Mars contact between their natal charts, while the composite places Venus and Mars far apart. There is no arithmetic contradiction: synastry compares A’s Venus to B’s Mars, while a composite first averages Venus with Venus and Mars with Mars, then compares those two new positions. Do not force one chart to confirm the other.
The reverse can also happen. Two derived composite planets may form a close aspect even when that exact planet pair does not cross from one natal chart to the other. It is a property of the derived construction. Read what was measured before assigning meaning. A result that looks surprising is a reason to inspect the degrees, orb, and midpoint convention.
A practical sequence
- Check each natal chart for date, time, place, and historical UTC offset.
- Compare the two charts and keep each planet’s owner visible.
- Read a few close contacts in the aspect library. If the hour is unknown, withhold houses and near-threshold lunar claims.
- Draw the composite with both natal charts to see exactly which positions made each midpoint.
- Ask whether the interpretation corresponds to how both people describe the relationship. If not, let it go.
And where does Davison fit?
A Davison chart is a third technique. It takes a midpoint of the two birth instants and a geographic midpoint, then calculates the planets for that derived time and place. A midpoint composite instead averages each matching natal longitude. Both produce one wheel, but their planet positions and house choices can differ. Use the relationship chart-type primer and Davison calculator when that is the method you intend to study.
Neither chart is a test of whether someone is trustworthy or whether a relationship will last. The real decisions belong to the people involved.
Synastry calculator →Clickable partner chart →House overlays →Composite + natal charts →