Calculating…
Synastry is the practice of comparing two natal charts to understand how two people's planetary placements interact with each other. Originating in Hellenistic astrology and refined through medieval and Renaissance traditions, synastry examines the angular relationships — conjunctions, trines, squares, oppositions, sextiles — between one person's planets and another's. When your Mars sits at 14° Scorpio and your partner's Venus sits at 16° Scorpio, that near-conjunction describes a specific energetic interaction: your drive and desire activates their values and sense of beauty. Synastry also examines house overlays — where your planets fall in the other person's chart houses, showing which life areas you most affect each other. Estrevia calculates synastry using the Lahiri ayanamsa, placing planets in their astronomically verified sidereal positions rather than the tropical approximation used by most Western astrology software.
When one person's Sun and another's Moon form a tight aspect — especially a conjunction or trine — the relationship carries an instinctive quality of recognition. The Sun person feels energized and purposeful around the Moon person; the Moon person feels emotionally secure and seen. In a Sun–Moon conjunction between two charts, the Sun person's identity and the Moon person's emotional needs are naturally attuned. Squares and oppositions introduce creative tension: the Sun's need for direction can collide with the Moon's need for emotional responsiveness. Over time, this friction can produce either growth or chronic misattunement, depending on how consciously both partners navigate it. Traditionally, Sun–Moon aspects are weighted most heavily in compatibility analysis — they reflect whether two people's core selves fundamentally resonate.
Venus and Mars across two charts map the chemistry of attraction. Venus describes what a person finds beautiful and how they draw others in; Mars describes how they pursue and what they desire. When person A's Venus aspects person B's Mars — particularly in conjunction, trine, or sextile — there is immediate magnetic pull. The Venus person is drawn; the Mars person pursues with an energy the Venus person finds welcome. Squares and oppositions create attraction complicated by friction: the desire is present but the styles of pursuit can clash, producing relationships that feel simultaneously compelling and exhausting. Extended analysis includes cross-chart Venus–Mars house overlays, which reveal not just whether attraction exists but which area of life becomes its primary arena — the 5th house (romance and play), the 8th house (deep bonding), or others.
Saturn aspects in synastry carry the most long-term weight. When person A's Saturn conjuncts, squares, or opposes person B's Sun, Moon, Venus, or Ascendant, an asymmetry enters the relationship: the Saturn person unconsciously adopts a structuring or restricting role; the other may feel both stabilized and constrained. Hard Saturn contacts (squares, oppositions) appear consistently in long-term partnerships alongside the harder dynamics — chronic criticism, a sense of being judged, or feeling one's growth is blocked. Trine and sextile Saturn contacts offer the binding quality of Saturn without its full weight: the relationship has staying power and seriousness, and both people feel the other is reliably present. Synastry researchers from John Addey to Robert Hand have noted that enduring relationships — for better or worse — tend to feature prominent Saturn contacts.
When two people share the same Moon sign — or whose Moon signs form a trine (signs of the same element) — their emotional rhythms align without effort. They cycle through moods in parallel, find comfort in similar domestic arrangements, and rarely need to explain their emotional responses because both already understand the register. In sidereal astrology, a shared Moon sign carries particular weight: both people were born when the Moon actually occupied that constellation, not a shifted approximation. Moon–Moon squares and oppositions describe a fundamental mismatch in emotional style — one partner withdraws when overwhelmed, the other escalates; one needs verbal reassurance, the other finds it intrusive. Without awareness of this mismatch, the friction compounds quietly over time rather than being resolved through conversation.
Estrevia's compatibility score weights aspects by category and orb. Sun–Moon, Moon–Moon, and Saturn–personal-planet contacts account for 60% of the total weight, reflecting their historical role as primary indicators of long-term resonance and challenge. Venus–Mars aspects contribute 25%, reflecting their role in physical and aesthetic attraction. Remaining interaspects make up the final 15%. Scores above 75 indicate strong multi-dimensional resonance — the charts interact favorably across multiple categories simultaneously. Scores between 45 and 75 describe selective compatibility: areas of genuine depth alongside areas that require deliberate navigation. Below 45 reflects fundamental differences in emotional style or life orientation. The score maps terrain, not destiny — two people with a score of 38 who understand the friction can build more consciously than two people with a score of 80 who ignore it.
The roughly 23° Lahiri ayanamsa shift can change the character of key synastry aspects. A Venus–Mars trine in tropical synastry might become a square in sidereal — or a Sun–Moon conjunction might separate into two different signs entirely. Sign placements shift too: if your partner's Sun is at 28° tropical Aries, it falls at approximately 5° sidereal Aries. One degree further west and the sidereal placement crosses into late Pisces, changing the sign-level interpretation completely. For a full explanation of why Estrevia uses sidereal positions and how the ayanamsa affects natal and synastry readings, see the Why Sidereal page.
The Sun–Moon axis is traditionally the strongest single indicator. It reflects whether one person's core identity resonates with the other's emotional baseline. Close Sun–Moon aspects — especially conjunction and trine — appear far more frequently in long-term partnerships than any other type of interaspect. Saturn–personal planet contacts rank second in importance, contributing the seriousness and longevity factor.
No synastry reading predicts outcomes with certainty. Synastry maps the energetic terrain — where resonance flows naturally and where friction is structural. A couple with strong Saturn contacts and challenging lunar aspects can build a lasting, conscious relationship. A couple with all trines and no Saturn contacts may lack the structure for sustained commitment. The chart describes tendencies, not destiny.
A double whammy occurs when two planets aspect each other reciprocally across both charts — for example, person A's Sun conjuncts person B's Moon, and person B's Sun trines person A's Moon. This mutual activation intensifies that particular dynamic in both directions, making it one of the most prominent themes in the relationship.
House overlays show where one person's planets fall in the other's houses, revealing which life areas the relationship activates. Your partner's Venus in your 7th house activates your sense of partnership; in your 2nd house, it touches your resources and values. Overlays add texture and context; interaspects remain the primary indicator of the relationship's energetic quality.
The ~23° Lahiri ayanamsa shift can change sign placements and, in some cases, convert one aspect type to another. A planet at 28° Scorpio tropical becomes roughly 5° Scorpio sidereal — the sign holds, but barely. At tropical 27° or earlier, the shift crosses a sign boundary into sidereal Libra, altering the entire sign-level interpretation in synastry.
Astrology is for personal reflection and entertainment purposes only. Nothing on this site constitutes medical, financial, legal, or psychological advice. Always consult a qualified professional for decisions affecting your health, finances, or wellbeing.
Compare two charts for astrological compatibility
Using Lahiri ayanamsa · Sidereal zodiac