Synastry is the astrological technique that compares two complete birth charts to see how two people relate — not just whether their sun signs match, but how their ten planets interact with each other. It's the real method behind the question "are we compatible?", and it goes far deeper than crossing two zodiac signs.
How it differs from sun-sign compatibility
Comparing sun signs (Aries with Leo, for example) is a quick approximation, but it only looks at 1 of each person's 10 planets — the same reason the sun sign isn't enough to know if you're compatible. Synastry overlays the two complete birth charts — with both people's time and place of birth — and looks at the exact angles their planets form with each other. That's where the real information appears: not "Aries and Leo match", but "your Venus forms a harmonious angle with their Mars" — a concrete fact about those two specific people, not a generalization about an entire sign.
What synastry looks at
- Venus and Mars crossed — the attraction and desire between the two.
- Moon with Moon (or with the other's Sun) — how emotionally comfortable the two people feel together.
- Mercury crossed — how they communicate, whether they "speak the same language" or clash when explaining themselves.
- Saturn crossed — where structure and commitment appear, or, if the angle is tense, weight and friction.
- Which house each of the other's planets falls in — not just the sign, but the life area the other person activates in you (7th house for partnership, 5th house for romance, 8th house for intimacy).
What you need for a real synastry reading
Just like with an individual birth chart, a serious synastry reading needs date, time, and place of birth for both people. Without both exact times, you can compare planets by sign (already useful information), but you lose the fine angles and the houses — which is usually where the detail lives that explains why a relationship feels a very particular way.
The first step of any synastry is your own birth chart
Before comparing two charts, it's worth knowing your own in depth: your ten planets, your houses, and your ascendant, calculated with real astronomical position.
Discover your birth chart →Frequently asked questions
What is synastry in astrology?
It's the technique that compares two complete birth charts — yours and another person's — to analyze how their planets relate to each other: what creates attraction, what creates friction, and which life areas each activates in the other.
Is synastry the same as sun-sign compatibility?
No. Sun-sign compatibility only compares one planet (the Sun) from each person. Synastry compares all ten planets of both complete birth charts, with their houses and exact angles — a much more detailed and specific analysis of those two particular people.
What information do I need to do a synastry reading?
Date, time, and place of birth for both people. Without exact times you can compare by sign, but you lose the houses and the fine angles between planets, which tend to be the most revealing part.
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