You have two complete birth charts, yours and someone else's. Separately, each describes a person. Together, they describe a relationship — and that is what synastry is: the art of reading two charts at once.
The tradition has a name for this overlap: synastry, or relationship astrology. It answers the questions people actually ask — why do we click, why do we clash, where do we support each other, where do we rub raw. The method is simple to learn and surprisingly deep to practice.
The Three Layers of Connection
When two charts meet, they interact in three distinct ways. Learn to read all three, and you will see the whole relationship, not just its chemistry:
- House overlays — where your planets fall in the other person's houses, and theirs in yours.
- Planetary aspects — how your planets gaze at their planets across the two wheels.
- The connection axis — how your 7th house (the house of partnership) relates to their Ascendant and theirs to yours.
Each layer answers a different question: overlays say what we mean to each other, aspects say how we feel when we are together, and the axis says whether we feel like partners at all.
House Overlays: What You Mean to Each Other
The single most useful tool in synastry is the overlay. Take each of your planets and find which house it occupies in their chart — then do the same for theirs in yours.
A simple example: your Venus in their 7th house. Their 7th house rules partnership, and Venus is the planet of love — so your presence becomes the relationship for them. They feel romantic when you are around. Your Saturn in their 2nd house is a different story: you bring structure or restriction to how they handle money and self-worth.
Every overlay is a sentence about the relationship, and the house is the subject of the sentence.
Planetary Aspects: How You Feel Together
The second layer is aspects between the two charts — the same rules of planetary sight you already know, applied across two wheels instead of one.
The most important cross-aspects are these:
- Venus–Moon — emotional sweetness; you make each other feel safe and cared for.
- Venus–Mars — physical and romantic chemistry; the classic attraction aspect.
- Moon–Moon — emotional compatibility; you instinctively understand each other's moods.
- Sun–Moon — the balance of roles; one leads with identity, the other with feeling, and the mix usually works.
Jupiter's cross-aspects protect the relationship; Saturn's test it; the nodes' gazes make it feel fated or karmic. Read the cross-aspects with the interpretation guide, and the chemistry of the relationship becomes legible.
The Connection Axis: Do You Feel Like Partners?
The deepest question in any relationship is whether the two of you actually occupy the role of partner for each other. The chart answers it with the connection axis.
The 7th house is the house of partnership, and the Ascendant is the self. When someone's planet falls in your 7th house — or your Ascendant falls in their 7th — they trigger your partnership instinct: you relate to them as a partner, not a stranger. When their Moon or Venus touches your Ascendant, they make you feel seen, which is the quiet foundation of attraction.
This axis is why two people can have excellent chemistry on paper and still feel like friends: the overlay and the aspects say comfort, but only the axis says partner.
The Moon and the Lunar Mansions
Emotional compatibility lives in the Moon — its sign, its house, and above all its lunar mansion. Two Moons in water signs resonate where two Moons in fire signs ignite; two Moons in the same element usually feel at home in each other's moods.
The 27 lunar mansions refine this further: a Moon in one partner's birth mansion that matches the other's emotional style is a quiet but powerful bond. When the Moon connections are strong, a relationship survives what the overlay cannot smooth over.
Compatibility Systems: Beyond the Two Charts
Synastry is one school of relationship reading; the tradition also has formal matching systems. The most famous is the Ashtakuta matching, the eightfold point system used in classical marriage consultation, which scores two birth Moons across eight dimensions.
The two approaches answer different questions. Synastry is diagnostic — it shows how two specific people interact. Ashtakuta is evaluative — it scores whether a match is favorable. Serious students use both: the point system for the verdict, synastry for the story.
How to Read Two Charts Together
- Draw or print both charts side by side, or use a synastry calculator that overlays them.
- List your planets in their houses, and theirs in yours. Circle the houses that receive three or more foreign planets — those are the strongest chapters of the relationship.
- Note the cross-aspects between your planets and theirs, especially Venus, Moon, Mars, and the Sun.
- Check the connection axis: which planets fall in each person's 7th house, and how the Ascendants relate.
- Read the mixture: strong overlays with easy aspects make a comfortable, compatible bond; strong overlays with tense aspects make an intense, growth-heavy one; no overlays at all make a relationship that stays on the surface.
Two charts in combination are more than the sum of their parts — they are a third thing, the relationship itself. For the formal scoring system used in traditional matchmaking, continue with Ashtakuta matching, and to see what your own chart promises about a future partner, read the 7th house and marriage.