Astrology 102 · 01 · Relationship
Synastry
How two birth charts interact, and what that says about any relationship
What synastry is
Synastry is the practice of overlaying two people's birth charts to see how their planets interact. When you place one person's chart on top of another's, you can see which of their planets fall on, oppose, square, or harmonize with the other's. Each contact tells a story about that dimension of the relationship.
The key principle is that planetary contacts between two charts activate both people. If your Mars lands on someone's Venus, they feel it too. The planet may be yours but the house it activates is theirs, and the aspects it makes to their natal planets shape how they experience you in that area of life.
What to look at first
Most astrologers start synastry with the Sun, Moon, Venus, and Mars, the personal planets that govern identity, emotion, love, and desire. Contacts between these four planets across two charts tell you most of what you need to know about the nature of the attraction and the emotional dynamics. From there, Saturn contacts reveal where commitment or pressure lives. North Node contacts show whether the relationship carries developmental weight.
The houses are equally important. When someone's Sun falls in your 7th house, they arrive into your life as a natural partner. When their Saturn falls in your 4th, they touch something deep in your sense of home and security. The house tells you where in your life you feel another person's planets.
Aspects in synastry
Conjunctions between two people's planets are the strongest contacts, a fusion of energy. Trines create ease and natural support. Sextiles bring opportunity and friendly rapport. Squares produce friction that is rarely comfortable but often keeps two people deeply engaged with each other. Oppositions create a push-pull dynamic where each person represents something the other needs but struggles to integrate.
A relationship with no squares or oppositions between key planets can feel comfortable but flat. Some of the most enduring relationships have significant challenging contacts alongside the harmonious ones. The friction is part of what makes the connection feel alive and worth sustaining.
Key synastry contacts
Sun conjunct Sun
HarmonyTwo people with the same Sun sign share a fundamental rhythm and direction. There is an ease of understanding, a recognition of each other's core drive. The risk is mirroring rather than complementing.
Sun conjunct Moon
Deep bondOne person's identity (Sun) aligns with the other's emotional core (Moon). This is one of the most binding contacts in synastry, often found in long-term partnerships. It creates strong empathy but can also produce dependence.
Venus conjunct Mars
AttractionMagnetic, often intensely physical attraction. One person's desire (Mars) meets the other's allure (Venus) directly. Common in romantic connections. The heat can sustain or burn depending on everything else in the chart.
Moon conjunct Moon
Emotional resonanceEmotional rhythms that naturally synchronize. These people feel comfortable together quickly and understand each other's moods without explanation. Strong in close friendships and family bonds as much as romance.
Saturn conjunct Sun/Moon
Pressure and commitmentThe Saturn person brings structure, expectation, and sometimes heaviness to the other's core identity or emotional life. Hard to ignore. At its best it creates long-lasting commitment; at its worst, it creates restriction and judgment.
Sun or Moon square each other
Productive frictionSquares between Sun and Moon placements create the kind of tension that keeps two people engaged. There is a fundamental difference in how they approach life that neither can simply ignore. Often more sustaining than constant agreement.
North Node conjunct a planet
Fated contactWhen one person's North Node touches the other's Sun, Venus, or Moon, many people describe the connection as feeling inevitable. These contacts often mark relationships that carry significant developmental weight for both people.
Venus conjunct Venus
Shared tasteAligned aesthetic sensibilities, similar ideas of beauty, pleasure, and what makes life enjoyable. This contact supports genuine friendship and harmony in shared daily life, whether romantic or not.
See how your chart connects with someone else's
A compatibility reading maps the key synastry contacts between two charts and explains what each one means for the relationship.
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