Comparing two birth charts
Synastry is a relationship-astrology technique that compares two natal charts directly. Instead of merging two people into one chart, it keeps Person A and Person B separate and measures the aspects formed from one chart to the other. With exact times, the comparison can also include angle contacts and house overlays. Without them, those time-sensitive layers should be withheld.
Quick reference
Keeping these layers distinct makes uncertainty visible and prevents a missing birth time from being hidden inside a confident-looking report.
| Layer | Question | How to use it |
|---|---|---|
| Planetary aspects | Which planets form a major angle? | Can be exact with precise data or uncertainty-aware when one birth time is unknown. |
| Angle contacts | Does a planet contact ASC or MC? | Require the chart with the angle to have a reliable exact birth time. |
| House overlays | Which house receives the other person’s planet? | Require a reliable house structure for the target chart. |
| Orb | How close is the aspect to exact? | AstroZora exposes the orb instead of hiding the geometry behind a score. |
| Certainty | Is the contact exact, confirmed or possible? | Unknown-time sampling can distinguish stable contacts from time-dependent ones. |
Synastry cannot repair a weak natal calculation. Historical timezone resolution, planetary longitudes and exact angles must be established independently for each person before cross-chart aspects are derived.
The calculation compares the longitude of each supported planet in Person A with each supported planet in Person B and classifies the major angular relationships that fall inside the documented orbs.
With both exact times, Person A’s planetary longitudes can be placed into Person B’s houses and vice versa. These are directional results: A’s Venus in B’s 7th house is not the same statement as B’s Venus in A’s 7th house.
For a missing birth time, AstroZora samples supported planetary positions across the local civil day. A contact that survives the uncertainty can be labeled confirmed. A contact that appears only for some possible times is labeled possible. Angle contacts and overlays are omitted.
Once the contacts are known, they can be organized into emotional connection, communication, attraction, relationship dynamics, long-term themes and potential friction. The categories are a reading aid, not a mathematical proof of relationship quality.
Worked method
If Person A’s Venus falls in Person B’s 7th house, the statement uses B’s house structure as the receiving frame. Reversing the charts can produce a completely different overlay. That directional distinction is why AstroZora calculates both A-in-B and B-in-A rather than treating an overlay as a symmetric match.
Use the concept in your chart
The fastest way to make this useful is to see the relevant placement or relationship in a calculated chart rather than reading generic descriptions in isolation.