What is synastry in astrology?
Synastry is a branch of astrology that studies compatibility between two people by comparing their natal charts. The method is based on analyzing cross-chart aspects — angular relationships between one partner's planets and the other's. Synastry helps understand relationship dynamics: where harmony arises, where tension exists, and where there's potential for growth. This method has been used by professional astrologers for over a thousand years and remains one of the most popular tools for relationship analysis.
How does the compatibility calculation work?
Our synastry calculator uses Swiss Ephemeris — the most accurate astronomical library, providing arcsecond precision. A natal chart is built for each partner based on their date, time, and place of birth. Then all aspects between planets of both charts are analyzed: conjunctions, trines, sextiles, squares, and oppositions. The result is a compatibility index showing the ratio of harmonious to tense interactions, along with a detailed list of the most significant aspects.
Types of aspects in synastry
Trine (120°) and sextile (60°) are harmonious aspects indicating natural understanding and ease of communication. Square (90°) and opposition (180°) are tense aspects that create challenges but simultaneously stimulate growth and transformation. Conjunction (0°) is the most powerful aspect that amplifies qualities of both planets, and can be either harmonious or challenging depending on the planets involved. Minor aspects (quintile, semi-sextile, quincunx) add nuance and detail to the overall picture.
The role of planets in synastry
The Sun and Moon are the foundation of compatibility: their aspects reveal basic character harmony and emotional connection. Venus governs romantic attraction and shared values, Mars — physical chemistry and energetic dynamics. Jupiter aspects bring optimism and expansion, Saturn — stability and responsibility (but sometimes restrictions). Outer planets (Uranus, Neptune, Pluto) point to deep transformational processes in relationships.