Two charts in relation
Synastry — from the Greek syn (together) and astron (star) — is the practice of comparing two by placing them in relation. One person's planets are measured against the other person's planets, , and . The result is not a score. It is a map of where two symbolic landscapes meet, and what happens at those meeting points.
The technique applies to any relationship: romantic partnership, friendship, family, creative collaboration. What changes is which chart factors carry the most weight.
What the overlay shows
Every contact in synastry describes a different kind of meeting. When one person's Moon falls in another's fourth house, home and interior life become shared territory. When one person's Saturn forms a square to another's Venus — a being the ninety-degree angle of tension and friction — there is a quality of pressure, discipline, or caution where the other person most wants ease and affection. When Jupiter sits on another person's Ascendant, it tends to expand and warm their self-presentation, sometimes to the point of excess.
None of these contacts is automatically good or bad. A Venus-Mars trine describes easy attraction; it does not promise endurance. A Saturn opposition to the Moon describes friction around emotional needs; it can also describe a structuring influence that makes the relationship workable over time. The in synastry carry the same dual nature they do in a natal chart.
How to read it
Begin with each chart separately. Synastry built on a shallow natal reading stays shallow. The natal chart sets the range of what a person can bring to a relationship.
Then compare in this order:
- Luminaries: Sun to Sun, Moon to Moon, Sun to Moon and back. Luminary contacts describe core recognition and emotional rhythm.
- Venus and Mars: attraction, desire, and the shape of wanting.
- Saturn: where one person steadies or burdens the other; the element of endurance.
- Angles: planets near another person's Ascendant or Descendant land with particular directness.
- House overlays: which houses one person's planets activate in the other chart.
Pay attention to repetition. One Venus-Mars trine describes attraction. If that attraction is also echoed in Moon-Venus contacts, house overlays into the fifth, and a shared element pattern, the theme is genuinely present. Single aspects tell partial stories.
The ethics of comparison
Synastry is a description, not a permission slip. Two charts with difficult contacts are not prohibited from relationship. Two charts with harmonious contacts are not guaranteed ease. The chart describes the structure of contact — what the bond will ask of each person — not whether they should or will sustain it.
Astrology reads what is there. The people living the relationship decide what to do with it.
The rule
Synastry reads where two lives make contact. The shape of that contact — easy or pressuring, central or peripheral — is what the technique names.