Synastry is the comparison of two natal charts: your planets laid over someone else's, aspect by aspect. It asks a narrower question than "are we compatible" — it asks how two people meet. Where does the contact feel effortless? Where does it consistently catch? What does each person activate in the other that neither reaches alone?
Sun-sign compatibility ("Leo and Aquarius: opposites attract") is the postcard version. It uses one point from each chart and ignores the other nineteen. Synastry uses both charts in full.
What the cross-aspects mean
Sun–Moon. One person's Sun touching the other's Moon is the classic "feels like home" contact: the identity of one lands directly on the emotional needs of the other.
Venus–Mars. Attraction and pursuit. Strong Venus–Mars contact explains chemistry that survives disagreement — and sometimes chemistry that outlives compatibility.
Moon–Moon. Two emotional weather systems compared. Harmonious contact reads as being soothed by the same things; hard contact reads as needing comfort in ways that do not translate.
Saturn contacts. Saturn to a personal planet brings weight: commitment, duty, and restriction in the same package. These are the aspects that make a relationship durable and, when they go wrong, the ones that make it feel like an obligation.
Ascendant contacts. Planets touching the other person's Ascendant show up as immediate recognition — the "I noticed you across the room" layer.
Houses. Which of your houses their planets fall into tells you what area of life they activate: the tenth (work and public life) plays very differently from the twelfth (private, unconscious, hidden).
Squares are not verdicts
The most common misreading of synastry is treating hard aspects as bad news. Squares and oppositions describe friction, and friction is also what makes a relationship generative rather than flat. A synastry chart with nothing but trines describes ease, not depth. What matters is whether the friction sits somewhere the two people can work with — and that is a question about them, not about the chart.
What Duetto computes
- Both natal charts, from each person's birth date, time (optional), and city, using the Swiss Ephemeris.
- The cross-aspect grid between the two charts, with orbs conventional for synastry work.
- House overlays in both directions — your planets in their houses, theirs in yours.
- A reading that starts from the strongest contacts and names, in plain language, where the relationship flows, where it grinds, and what each of you tends to draw out of the other.
You add a partner by entering their birth details. Birth time is optional for both people; without it, house overlays and Ascendant contacts are dropped rather than guessed, and the reading says so.
A note on consent: you are entering someone else's birth data. Ask them first. Their data is protected exactly as yours is, and you can delete a partner at any time — see the Privacy Policy.
Where it goes next
Synastry describes how two people meet. The composite chart asks a different question: what the relationship is as its own thing. Both are built on the natal chart, and daily transits then show what the current sky is stirring in either of you.
Duetto is for entertainment and reflection, not relationship advice.