Synastry is the astrological technique of comparing two natal charts to understand the dynamics of a relationship. By overlaying one person's planets onto another person's chart, synastry reveals areas of attraction, conflict, growth, and lasting connection.
What Synastry Shows
Synastry goes far beyond basic Sun sign compatibility. It examines how every planet in one chart interacts with every planet and house in the other chart. The result is a detailed map of the relationship's strengths, challenges, and evolutionary potential.
The Most Important Synastry Aspects
Sun-Moon Connections When one person's Sun aspects the other's Moon, there is a natural sense of understanding. The Sun person feels seen and supported, while the Moon person feels emotionally nourished. Conjunctions and trines are the most harmonious. Squares create tension that can be growth-producing if both partners are willing to work.
Venus-Mars Aspects Venus-Mars contacts generate physical and romantic attraction. Venus conjunct Mars creates immediate chemistry. Venus trine Mars produces easy, flowing romantic energy. Venus square Mars generates passionate tension — exciting but sometimes volatile.
Moon-Moon Aspects How the two Moons interact reveals emotional compatibility. Harmonious Moon aspects mean the couple naturally understands each other's emotional needs. Challenging Moon aspects mean they process feelings differently and must learn to accommodate.
Saturn Aspects Saturn contacts in synastry indicate longevity and commitment — but also restriction. Saturn conjunct Venus can mean lasting love with occasional feelings of duty or limitation. Saturn square Mars can create frustration over pace and timing. Some Saturn is necessary for a relationship to endure; too much makes it feel like an obligation.
Pluto Aspects Pluto contacts create intensity and transformation. Pluto conjunct Venus or Mars produces magnetic, obsessive attraction. These relationships change both people permanently, for better or worse.
House Overlays
Where one person's planets fall in the other person's houses reveals which areas of life are activated by the relationship. If your partner's Venus falls in your 10th house, they may enhance your career or public image. If their Mars falls in your 4th house, they energize your home life — or create domestic tension.
The Composite Chart
While synastry compares two separate charts, the composite chart combines them into a single chart representing the relationship as its own entity. The composite chart shows what the relationship produces when both people are together, regardless of their individual charts.
Red Flags in Synastry
- ✦Pluto square personal planets — potential for power struggles and manipulation
- ✦Saturn square Venus — love that feels heavy or dutiful rather than joyful
- ✦Mars square Mars — constant competition and conflict
- ✦Neptune conjunct personal planets — idealization that prevents seeing the partner clearly
- ✦No major aspects at all — possible lack of significant connection
Green Flags in Synastry
Not all synastry is about red flags. Here are the aspects that indicate strong, healthy relationship potential:
- ✦Sun trine Moon — Natural understanding where one person's identity nourishes the other's emotional world
- ✦Venus conjunct Jupiter — Generous, expansive love that makes both people feel lucky
- ✦Moon trine Moon — Emotional rhythms that naturally synchronize, creating effortless domestic harmony
- ✦Sun conjunct Descendant — One person literally embodies the other's ideal partner archetype
- ✦North Node conjunct personal planets — A relationship with evolutionary purpose that helps both people grow
Timing in Synastry
Synastry is static — it shows the permanent dynamics between two charts. But transits to the synastry contacts activate different themes at different times. When transiting Saturn crosses a Venus-Mars contact in synastry, the couple faces tests of commitment. When transiting Jupiter crosses it, the relationship expands joyfully. Understanding both the synastry AND the current transits gives a complete picture of any relationship moment.
Synastry vs Other Compatibility Methods
How synastry compares to other astrological compatibility techniques:
- ✦Synastry vs Composite Chart — Synastry overlays two separate charts to see how INDIVIDUALS affect each other, preserving each person's identity in the analysis. The composite chart blends both charts into ONE chart representing the relationship itself as an entity. Synastry shows how you interact; the composite shows what the relationship IS. Both are essential for a complete picture.
- ✦Synastry vs Sun Sign Compatibility — Sun sign compatibility considers only one placement out of dozens in each chart. Synastry considers ALL planetary contacts, house overlays, and aspect patterns. Sun sign compatibility is a rough sketch; synastry is the detailed architectural blueprint of the relationship.
- ✦Synastry vs Davison Chart — The Davison chart calculates the midpoint in time and space between two births, creating a chart for the relationship's metaphorical birth moment. Synastry keeps the two charts separate for comparison. The Davison chart can be progressed and transited like a natal chart, giving the relationship its own timeline.
- ✦Synastry vs Vedic Compatibility (Ashtakoot) — Vedic astrology uses an eight-factor scoring system based on Moon sign and nakshatra, producing a numerical compatibility score out of 36. Western synastry is more nuanced and detailed but less systematic. Vedic gives you a SCORE; synastry gives you a STORY.