Synastry

Origin and etymology

"Synastry" derives from the Greek syn ("together") and aster ("star"): literally, "stars together" or "comparison of stars". The practice of comparing natal charts to evaluate relationships is as old as astrology itself: marriage between aristocratic families in Rome, in the imperial Chinese court, in Renaissance European nobility, was frequently consulted with astrologers before being arranged, comparing the two betrothed's charts.

In the 20th century, authors like Donna Cunningham, Stephen Arroyo and Liz Greene systematised modern psychological synastry. The basic technique: superimpose the two natal charts (sometimes literally, in a circular graph) and observe the cross aspects between the planets of one person and those of the other. Each aspect tells a dynamic of the bond.

Layers of synastry

A complete synastry examines several layers. Sun-Sun: basic chemistry between identities. Moon-Moon: emotional and domestic compatibility (decisive long-term). Venus-Mars: erotic and sexual chemistry. Mercury-Mercury: how they understand each other mentally. Saturn to any planet: karmic test dynamics. Each combination has its nuances according to the aspects formed.

The favourable cross aspects (trines and sextiles between their planets) indicate fluidity and harmony. The tense aspects (squares and oppositions) generate friction that can be productive (forces growth) or destructive. The conjunctions (planets in the same degree) are the most intense aspects: they amplify whatever they touch, for better or worse. A rich synastry is never just "good" or "bad": it is a nuanced map.

Difference with solar sign compatibility

Complete synastry is very different from compatibility by solar sign ("Aries and Libra are compatible"). That basic reading only looks at one planet of each, ignoring the other nine and all the aspects. A real synastry requires both complete natal charts with exact birth time. Its precision is notably greater: it explains why two people with "incompatible" solar signs get along very well, or why a couple with good initial chemistry wears down after months.