Synastry
Chart Calculator
Compare two birth charts to discover your cosmic compatibility — the cross-aspects, magnetic connections, and growth edges that define your relationship.
What Is Synastry in Astrology?
Synastry is the art of comparing two birth charts to reveal the energetic dynamics between two people — the magnetic pulls, the friction points, the areas of effortless harmony, and the growth edges that define any significant relationship.
Unlike sun-sign compatibility (which compares only one of the dozens of placements in your chart), synastry examines every planet in each person's chart against every planet in the other's. The angular relationships between these planets — called cross-aspects — paint a nuanced, multi-dimensional picture of how two people interact at the deepest levels.
A synastry reading can illuminate why you feel instantly comfortable with someone, why certain people trigger your deepest vulnerabilities, or why a relationship that "should" work on paper feels flat. The chart reveals what the personality test cannot: the energetic chemistry between two souls.
☌ Cross-Aspects
The angular relationships between one person's planets and the other's. Conjunctions (0°), trines (120°), squares (90°), oppositions (180°), and sextiles (60°) each tell a different story about how the energy flows — or clashes — between two people.
⊕ Bi-Wheel Chart
The bi-wheel (or composite overlay) places Person A's chart on the inner ring and Person B's on the outer. Aspect lines connecting between the rings reveal the cross-chart connections at a glance — the visual fingerprint of your relationship.
The Most Important Synastry Aspects
☉ Sun – ☽ Moon
The Luminaries. Sun-Moon connections are the single most important indicator of fundamental compatibility. When one person's Sun harmonizes with the other's Moon, there is an instinctive feeling of "belonging" — the conscious self and the emotional self speak the same language.
♀ Venus – ♂ Mars
The Love-Desire Axis. Venus-Mars aspects are the classic indicators of sexual and romantic chemistry. Venus represents what you find beautiful and desirable; Mars represents your drive to pursue. Their interaction determines the quality and intensity of physical attraction.
☽ Moon – ☽ Moon
Emotional Compatibility. Moon-Moon aspects reveal how two people's emotional natures interact. Harmonious Moon aspects create deep emotional comfort and domestic harmony. Challenging Moon aspects create friction around emotional needs, security, and how each person processes feelings.
♄ Saturn Aspects
Commitment & Karma. Saturn aspects in synastry indicate where the relationship has karmic weight. Saturn conjunctions and trines create deep commitment, loyalty, and longevity. Saturn squares can feel restrictive but often indicate a relationship you are "meant" to learn from.
Synastry vs. Composite vs. Davison Charts
Synastry, composite charts, and Davison charts are the three pillars of relationship astrology. Each answers a different question:
Synastry
How do you experience each other? Synastry compares two separate charts to see how each person's planets activate the other's. It reveals attraction, friction, growth, and challenge between two individuals.
Composite
What is the relationship itself? A composite chart calculates the midpoints of each pair of planets to create a single blended chart — the relationship as its own entity with its own purpose and challenges.
Davison
When and where did the relationship "begin"? The Davison chart calculates the midpoint in time and space between two births, producing a real chart for a real moment — giving the relationship an actual birth chart with valid house cusps and transits.
Most professional astrologers use all three: synastry to understand the dynamics between the individuals, the composite to understand the relationship entity, and the Davison to track the relationship's evolution through transits and progressions over time.
Understanding Cross-Aspects
Conjunction (0°)
Two planets in the same degree fuse their energies. The effect depends on the planets involved — Venus conjunct Mars is electric attraction; Saturn conjunct Moon may feel heavy. Conjunctions are the most powerful aspect type.
Trine (120°)
Harmonious flow between two planets. The energies support each other effortlessly. Trines bring ease, comfort, and natural compatibility — though they may lack the dynamic tension that drives growth.
Square (90°)
Friction and challenge between two planets. The energies are at cross-purposes, creating tension that can be either destructive or profoundly growth-inducing. Squares generate passion and prevent stagnation.
Opposition (180°)
Polarity and magnetism between two planets. Each person embodies what the other needs to develop. Oppositions create powerful attraction but also projection — seeing in the other what you cannot see in yourself.
Sextile (60°)
Opportunity for harmony. Milder than a trine, the sextile offers potential for pleasant interaction that requires some effort to activate. Sextiles are the "friendly handshake" of aspects.
Your Sun Sign in Synastry
Each Sun sign brings unique gifts and challenges to synastry. Expand your sign below to discover how your solar identity interacts with a partner's chart.
♈Aries Sun in Synastry
Aries Sun in synastry brings bold, direct energy to relationships. You activate your partner's courage and initiative. Your Mars-ruled nature craves partners who can match your intensity without trying to tame it. Sun-Moon connections with Water signs often create a steamy, emotionally charged dynamic, while Fire sign trines feel instantly familiar.
♉Taurus Sun in Synastry
Taurus Sun brings stability, sensuality, and devotion to synastry. Your Venus-ruled nature values loyalty and physical affection above all. Partners whose Moon or Venus touches your Sun feel immediately comforting. You ground restless partners and bring earthy pleasure to the relationship, but may clash with those who crave constant change.
♊Gemini Sun in Synastry
Gemini Sun electrifies synastry with curiosity, wit, and mental stimulation. Mercury-ruled and dual-natured, you need a partner who can keep up intellectually. Sun-Mercury cross-aspects are especially powerful for you — they create the verbal chemistry that keeps you engaged. Air and Fire sign connections spark your communicative brilliance.
♋Cancer Sun in Synastry
Cancer Sun brings deep emotional nurturing to synastry. Moon-ruled and intuitive, you create emotional safety for your partner and seek the same in return. Sun-Moon conjunctions and trines with your chart are marriage indicators. Your protective instinct can heal partners with difficult childhood wounds, but you need reciprocal emotional care.
♌Leo Sun in Synastry
Leo Sun radiates warmth, generosity, and creative passion in synastry. Sun-ruled and magnetic, you need to be admired — and you'll lavish your partner with devotion in return. Venus touching your Sun creates adoration. Jupiter aspects expand your shared joy. Partners who celebrate your light (rather than competing with it) bring out your most generous self.
♍Virgo Sun in Synastry
Virgo Sun brings thoughtful devotion and practical care to synastry. Mercury-ruled and service-oriented, you show love through acts of helpfulness and attention to detail. Sun-Venus aspects create a refined, elegant connection. You ground dreamy partners and bring order to chaotic lives, but must guard against criticism replacing affection.
♎Libra Sun in Synastry
Libra Sun is the natural diplomat of synastry — Venus-ruled, beauty-loving, and partnership-oriented. You seek harmony, fairness, and aesthetic alignment with a partner. Sun-Venus cross-aspects are your sweet spot: they create instant mutual admiration. You excel at compromise but may struggle with partners who thrive on conflict as a bonding mechanism.
♏Scorpio Sun in Synastry
Scorpio Sun brings transformative intensity to synastry. Pluto-ruled and emotionally penetrating, you don't do surface-level connections. Sun-Pluto cross-aspects create obsessive, fated-feeling bonds. Venus or Mars touching your Sun ignites volcanic passion. You demand emotional truth from partners and offer profound loyalty to those who earn your trust.
♐Sagittarius Sun in Synastry
Sagittarius Sun brings adventure, philosophy, and expansive optimism to synastry. Jupiter-ruled and freedom-loving, you need a partner who grows alongside you rather than anchoring you down. Sun-Jupiter cross-aspects feel blessed and abundant. Fire sign connections share your enthusiasm, while Air signs fuel your intellectual wanderlust.
♑Capricorn Sun in Synastry
Capricorn Sun brings ambition, commitment, and quiet strength to synastry. Saturn-ruled and long-term oriented, you take relationships seriously and expect the same. Sun-Saturn cross-aspects, often feared, are actually your comfort zone — they create the structure and accountability you thrive in. You build empires with the right partner.
♒Aquarius Sun in Synastry
Aquarius Sun brings intellectual freedom, progressive ideals, and unconventional love to synastry. Uranus-ruled and future-oriented, you need a partner who respects your independence and shares your humanitarian vision. Sun-Uranus cross-aspects create electric, awakening connections. You teach partners to think beyond convention and love beyond possession.
♓Pisces Sun in Synastry
Pisces Sun brings spiritual depth, empathy, and creative sensitivity to synastry. Neptune-ruled and boundaryless, you merge emotionally with partners in ways that can be transcendent or overwhelming. Sun-Neptune cross-aspects create soulmate feelings — an almost psychic bond. You need a partner who values your sensitivity rather than exploiting it.
Frequently Asked Questions
Do I need exact birth times for synastry?
Exact birth times allow for the most accurate analysis, including house overlays and precise Moon positions. However, synastry can still be highly informative without exact times — most planetary positions (except the Moon, which moves 12-14° per day) are stable regardless of birth time.
Are challenging aspects bad for relationships?
No. Challenging aspects (squares and oppositions) create dynamic tension that can be incredibly growth-inducing. Many astrologers consider a mix of harmonious and challenging aspects ideal — the harmony provides comfort and ease, while the challenge provides passion and motivation to grow. Relationships with only harmonious aspects may lack the spark that keeps things alive.
What does the harmony score mean?
The harmony score is the ratio of harmonious aspects (trines, sextiles) to challenging aspects (squares, oppositions). A score of 70%+ indicates a naturally flowing connection. Below 40% suggests significant areas of friction. However, this is just one metric — the specific planets involved matter more than the overall count.
Can synastry predict if a relationship will last?
Synastry reveals potential and dynamics, not destiny. Strong Saturn aspects often indicate longevity, while harmonious Sun-Moon and Venus-Mars aspects indicate compatibility. But free will, emotional maturity, and life circumstances all play roles that no chart can predict. Synastry shows what you're working with — what you build is up to you.
Does synastry work for non-romantic relationships?
Absolutely. Synastry is valuable for understanding any significant relationship — friendships, business partnerships, parent-child dynamics, even the relationship between a person and a place. The planets involved simply express differently: Venus-Mars may indicate creative rather than romantic chemistry in a professional context.
Explore Your Complete Chart
Your synastry reveals the relationship — but your natal chart reveals you. Generate your full birth chart to understand the individual strengths you bring to every connection.