Synastry

Synastry overlays one person's chart onto another's to examine how their planets interact. When one person's Venus conjuncts another's Mars, there's often strong romantic and physical attraction. When one person's Saturn squares another's Moon, emotional coldness or restriction may be felt. The most significant synastry aspects typically involve personal planets (Sun, Moon, Mercury, Venus, Mars) touching the other person's personal planets or angles (Ascendant and Midheaven). Outer planet contacts — especially Pluto — can indicate transformative but intense connections. Beyond individual aspects, astrologers also use composite charts (which merge two charts into one) and Davison charts (which find the midpoint in time and space between two births) to understand the relationship as its own entity. Synastry reveals potential, while the individuals involved choose how to fulfill or squander it.

The word synastry comes from the Greek syn (together) and astron (star) — literally, stars together. Hellenistic astrologers were comparing charts as early as the 1st century CE, and Ptolemy's Tetrabiblos (c. 150 CE) laid out principles of planetary compatibility that later practitioners built on. The technique developed further in medieval Arabic astrology, where comparing the positions of Venus and Mars between two charts became standard practice. Renaissance astrologers in Europe refined the method, and by the 17th century synastry was a recognized tool for assessing marriage prospects. The modern framework — overlaying two natal charts and reading house placements alongside aspects — was largely systematized in 20th-century Western astrology.

Generate a synastry chart on Astro.com (Extended Chart Selection → Synastry) or Astro-Seek using both partners' accurate birth times. The chart displays the two natal charts overlaid plus the inter-chart aspects. Stephen Arroyo's *Relationships and Life Cycles* (1979) is the standard introductory synastry reference; Liz Greene's *Relating: An Astrological Guide to Living with Others* (1977) gives the deeper psychological reading; Sue Tompkins's *Aspects in Astrology* (1989) covers the aspect-by-aspect interpretation. The aspects with the most empirical interpretive weight in case-study astrology are tight (≤3° orb) aspects between personal planets and angles — Venus–Mars and Moon–Moon contacts get the most attention in the relationship literature, but Sun–Saturn and Saturn–Moon contacts tend to be the most predictive of long-term dynamics.