Synastry is the astrological technique of comparing two birth charts to understand how two people affect each other. Not who they are separately, but what happens in the space between them - where the energy flows, where it stalls, where friction and depth come from.
What Synastry Actually Measures
Every planet in your chart occupies a specific degree of the zodiac. When someone else's planet lands at or near that same degree - or at a mathematically significant angle to it - the two planets are in aspect. That aspect is what synastry reads.
A Venus-Mars conjunction between two people (where one person's Venus occupies the same degree as the other's Mars) is the classic signature of physical attraction and creative combustion. The orb - the distance in degrees between the two points - determines how tightly the aspect operates. A 2-degree orb is tight and prominent; an 8-degree orb is present but diffuse.
The five dimensions this reading assesses - love, communication, values, passion, and trust - each draw from a cluster of the most relevant cross-chart aspects. Love draws from Venus-Moon and Venus-Venus contacts. Communication pulls from Mercury aspects across the two charts. Trust is largely Saturn-related: Saturn conjunct or trine personal planets in the other chart can create enduring commitment; Saturn square Moon creates emotional friction that requires conscious work.
How to Read the Compatibility Scores
Each score is a weighted average of the aspects that feed that dimension. A score of 80+ means the planets involved are in harmonious aspect and the energy in that area flows with relative ease. A score below 50 means there are tense aspects at play - squares and oppositions that create friction, misunderstanding, or push-pull dynamics.
A low score is not a bad relationship. Some of the most electrically alive connections are built on tension aspects - the Sun opposite Moon, the Mars square Pluto. Tension means there is something to navigate, work through, and potentially transform. Easy aspects (trines and sextiles) feel comfortable but do not always generate the intensity that holds people together over time.
The Key Cross-Aspects to Watch
Sun-Moon contacts are the foundation. When one person's Sun touches the other's Moon - whether by conjunction, trine, or opposition - there is a fundamental resonance between who they are at their core and what the other needs emotionally. This is the aspect most associated with long-term compatibility.
Saturn contacts to personal planets (Sun, Moon, Venus, Mars) are the commitment signatures - but they cut both ways. Saturn trine Venus stabilizes and deepens a relationship. Saturn square Moon makes the emotional life of the relationship feel contracted, restricted. Neither is fatal, but both are important to see clearly.
Venus-Pluto contacts are worth noting in any romantic synastry. They indicate intensity, transformation, and the kind of love that changes both people. The trine version is magnetic and growth-producing; the square or opposition version is magnetic and potentially consuming. Both are real.
Enter both birth dates, cities, and times to get the full cross-aspect picture.
