What Is Synastry? Relationship Astrology Explained
June 13, 2026 · 5 min read
Synastry is the branch of astrology that compares two people's birth charts to understand their relationship. It's how astrologers go beyond “what are your signs?” to see how two whole personalities actually interact.
How synastry works
Instead of judging a couple on sun signs alone, synastry looks at how each person's planets connect to the other's. Where your Venus meets their Mars, or your Moon meets their Sun, shows where you harmonise, where you spark, and where you'll need to work.
The placements that matter most
Your Moon signs reveal emotional compatibility, your Venus signs show how you each love, and your Sun signs show how your core identities fit. The Ascendants and Mars placements add attraction and chemistry. Together they paint a far richer picture than star-sign matching.
Synastry vs composite charts
Synastry compares two separate charts. A composite chart merges them into a single chart that represents the relationship itself as a third entity. Many astrologers use both — synastry for how you interact, composite for the relationship's own purpose.
Trying it yourself
You don't need to be an astrologer. Enter two sets of birth details into a synastry calculator and it compares the charts for you, scoring how your Sun, Moon and Venus connect — a great starting point for understanding any relationship.
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