Synastry

Definition

Pronunciation: SIN-uh-stree

Also spelled: Chart Comparison, Relationship Astrology, Inter-Chart Analysis

From Greek synastria (conjunction of stars, a shared stellar fate), the astrological technique of comparing two natal charts by examining the aspects formed between one person's planets and another's. The technique reveals the felt dynamics between two people -- where they harmonize, where they clash, and what each activates in the other.

Etymology

Greek synastria combines syn- (together, with) + astron (star), literally 'being under the same stars' or 'sharing a stellar configuration.' The term was used in Hellenistic Greek to describe the astrological compatibility assessment of two people, typically for marriage. Arabic astrologers used the concept within their extensive treatment of marriage elections (choosing auspicious times for weddings) and compatibility assessment. The modern English 'synastry' was revived in the twentieth century by astrologers seeking a technical term for chart comparison distinct from the composite chart technique.

About Synastry

Synastry works by overlaying two natal charts and examining the aspects that form between one person's planets and the other's. When Person A's Venus at 15 degrees Taurus forms a trine to Person B's Moon at 14 degrees Virgo, the astrologer reads this as a harmonious emotional-aesthetic connection: A's way of loving and valuing (Venus) flows easily with B's emotional nature and instinctual responses (Moon). When A's Mars at 20 degrees Scorpio squares B's Saturn at 22 degrees Aquarius, the reading indicates friction: A's assertive drive meets B's structural boundaries, producing either productive discipline or chronic frustration.

The technique predates its modern name. Dorotheus of Sidon (1st century CE) provided extensive guidance on assessing marriage compatibility through chart comparison in his Carmen Astrologicum. His method examined the relationship between the luminaries (Sun and Moon) of both partners, the condition of the seventh house rulers, and the Venus and Mars placements. Dorotheus's approach was pragmatic: he sought to predict whether a marriage would be harmonious, difficult, or short-lived, and his criteria were specific enough to produce definitive judgments.

Ptolemy discussed marriage timing and compatibility in Tetrabiblos IV, focusing primarily on the luminaries: the man's Sun-Moon relationship to the woman's Sun-Moon configuration determined the basic quality of the bond. This luminary-based approach -- assessing the compatibility of the two charts' Sun-Moon dynamics -- remained central through the medieval period and persists in modern practice. The Sun-Moon contacts between two charts describe the fundamental life-force and emotional compatibility of the relationship.

William Lilly addressed relationship questions primarily through horary astrology (casting a chart for the moment the question is asked) rather than synastry per se. However, his rules for assessing the condition of the first-house ruler (the querent) and the seventh-house ruler (the partner) in relationship questions established principles that synastry practitioners later adopted: mutual reception (when each ruler is in the other's sign of dignity) indicated mutual benefit; affliction between the rulers indicated difficulty.

The modern psychological approach to synastry was developed primarily by Liz Greene, Robert Hand, and Stephen Arroyo. Greene's Relating (1978) established the framework that relationship astrology is fundamentally about projection and integration -- we attract partners who carry our disowned planetary energies. A man with an unaspected Moon may gravitationally draw partners whose Moon is prominent, seeking through the relationship the emotional connection he cannot easily access within himself. Greene demonstrated that the most magnetic synastry contacts are often the most psychologically charged: they indicate where each person triggers the other's unconscious material.

Robert Hand's Planets in Composite (1975) introduced the composite chart technique as a complement to synastry. While synastry examines inter-chart aspects (my planets to your planets), the composite chart creates a single chart from the midpoints of both charts' corresponding planets, producing a third chart that describes the relationship itself as an entity. The composite Sun, for instance, is the midpoint of both partners' natal Suns, and its sign, house, and aspects describe the relationship's core identity and purpose. Modern relationship astrologers typically use both techniques: synastry for the felt dynamics between the individuals, and the composite for the relationship's own character.

The most significant synastry contacts involve the personal planets (Sun, Moon, Mercury, Venus, Mars) and the angles (Ascendant and Midheaven). Outer planet contacts (one person's Pluto to another's Venus, for example) indicate transformative, often difficult dynamics that operate at a deep psychological level. The Saturn contacts are particularly telling: Saturn aspects between charts indicate where one person's structure, discipline, or limitation meets the other's energy. Saturn conjunct or square another's personal planet produces a sense of weight, responsibility, and sometimes restriction in the relationship. Saturn trine or sextile produces stability, commitment, and longevity.

The 'double whammy' -- a synastry contact that operates in both directions (A's Venus aspects B's Mars, and B's Venus also aspects A's Mars) -- is considered especially significant because the energy exchange is reciprocal. Both people feel the same dynamic, though from different sides. Double whammies involving Venus-Mars indicate strong mutual physical attraction; those involving Sun-Moon indicate deep mutual recognition; those involving Saturn-personal planets indicate mutual karmic or developmental significance.

Vedic astrology approaches relationship compatibility through kundali matching (also called guna matching or ashtakoot), a systematic scoring system that evaluates eight categories of compatibility between two charts. The system assigns points based on Moon sign (rashi), Moon nakshatra (lunar mansion), and other factors, with a maximum score of 36. Scores above 18 are considered acceptable for marriage. This systematic, quantitative approach differs from Western synastry's more interpretive, nuanced style, though both traditions consider the Moon's condition paramount in assessing emotional compatibility.

Modern synastry practice has expanded beyond romantic relationships. Parent-child synastry reveals the dynamics between parent and child that shape development. Business partnership synastry assesses professional compatibility. Family synastry maps the interaction patterns within a household. The technique applies wherever two people interact closely enough that their natal patterns engage each other's unconscious material -- which, in practice, means any sustained relationship of significance.

Significance

Synastry addresses the question that brings more people to astrologers than any other: 'Will this relationship work?' The technique's enduring appeal reflects a deep human need to understand the invisible dynamics that make some relationships effortless and others excruciating. By providing a symbolic language for these dynamics, synastry offers both insight and vocabulary -- it helps people articulate experiences that are felt powerfully but are difficult to name.

Liz Greene's integration of Jungian psychology with synastry transformed relationship astrology from a compatibility checklist into a tool for understanding projection, shadow work, and psychological growth through partnership. Her framework -- that we attract what we need to integrate -- gave synastry therapeutic depth and made it one of the most powerful applications of the astrological model.

The development of the composite chart by Hand added a dimension that synastry alone could not provide: a description of the relationship as an entity with its own character, purpose, and developmental arc. The combination of synastry (how individuals experience each other) and composite analysis (what the relationship itself is becoming) represents modern relationship astrology's most complete toolkit.

Connections

Synastry examines the aspects formed between two natal charts, making it dependent on accurate birth data for both individuals. The most impactful contacts involve conjunctions and oppositions to personal planets and angles.

Contacts to the Ascendant indicate visceral, identity-level impact; contacts to the Midheaven affect career and public life. Transits to the composite chart (the midpoint chart derived from both natal charts) time relationship developments.

The Vedic equivalent is kundali matching, practiced within Jyotish using a systematic scoring system based on the Moon's position. Both traditions prioritize lunar compatibility -- the emotional, instinctual dimension of the bond -- as the foundation of relationship assessment.

See Also

• Aspect
• Conjunction
• House System
• Natal Chart
• Opposition
• Transit

Further Reading