Synastry

sin-ASS-tree

Definition

Synastry is how astrologers compare two people's birth charts to understand the relationship between them — a couple, a parent and child, two colleagues. You lay the charts over each other and read four kinds of contact: aspects between planets across the two charts, each person's planets falling into the other's houses (the house overlays), contacts to each chart's angles, and the way the two chart rulers answer each other. Both charts stay whole — synastry never blends them into a new, third chart.

In Tradition

Most modern Western astrologers treat synastry as the main way to read a two-person relationship, working alongside the composite and Davison charts, which do blend the two into one. The thinking runs like this: each person's own patterns get switched on and turned up when they meet the other's. Practitioners lean hardest on the personal planets and the angles. Saturn and the outer planets tend to be read as what holds a bond together, idealises it, or transforms it.

In Practice

To work a synastry comparison, you first cast both charts the same way, then build a grid of every aspect between a planet in one chart and a planet in the other, using moderate orbs — usually 6° or less for the Sun and Moon and the personal planets, tighter for the slow outer planets. You note where each person's planets fall in the other's houses, and any contact to the angles. You follow each chart's ruling planet across both wheels, and you re-weigh any planet that picks up a close cross-chart contact. Aspects that echo back the other way — the double whammy — get flagged. The overall balance of elements and modes between the two charts gives a temperament-level read, while specific Venus-Mars and Sun-Moon contacts tend to describe the felt charge of the relationship.

Historical Origin

The idea of comparing two charts is old — Ptolemy's Tetrabiblos IV.5 (2nd century CE) already weighs friendship and enmity by comparing two people's Suns, Moons, and angles. But synastry as a full method is a 20th-century Western development. Liz Greene's Relating (1977) drew the psychological reading of cross-chart aspects together into one influential, still-cited book, and Robert Hand, Howard Sasportas, Stephen Arroyo, and Steven Forrest built out the practical detail.

Definition

In Tradition

In Practice

Historical Origin

Further Reading