Synastry

Synastry (from the Greek syn, "together," and astron, "star") is an astrological technique for analyzing compatibility: two natal charts are laid over each other, and you look at what aspects one person's planets form with the other's planets and houses. One person's Venus in an easy aspect with the other's Moon, for example, often describes warm emotional rapport, while a tense Saturn aspect to a partner's personal planets can point to a sense of restriction or a test of endurance over time. Synastry doesn't hand down a "compatible / not compatible" verdict — instead, it shows a map of potential themes: where the relationship is likely to come easily and where it will call for conscious effort and dialogue. Separate from synastry, there's also the composite chart technique (a single "relationship chart," rather than an overlay of two), which describes the pair as a system in its own right. For self-knowledge, synastry is useful not as a tool for picking a partner by calculation, but as a language for talking about a relationship that already exists: seeing in the aspects a confirmation of what both partners already sense intuitively, and discussing it directly instead of guessing.