What is a Synastry Chart?

The technique of placing two people's birth charts on the same wheel and looking at the aspects one person's planets make to the other's. This is the oldest and most widely used method in relationship astrology.

How it works

In synastry the two charts are not merged — they are overlaid. Which sign and house does person A's Venus land in within person B's chart? How many degrees of aspect does B's Mars make to A's planets? Each comparison forms its own sentence; the chart is the sum of those sentences.

One person's planet falling into another's house is its own piece of information: if A's Sun lands in B's 7th house (the house of relationships), B experiences this relationship as part of the theme of partnership in their own life.

Which aspects stand out

Aspect	Usual meaning
Conjunction (0°)	Intense; a theme so intertwined the two can barely be told apart
Trine / Sextile (120° / 60°)	Easy flow, natural compatibility
Square (90°)	Friction — but also pressure to grow
Opposition (180°)	Attraction AND tension together; "completing opposites"

Aspects between personal planets (Sun, Moon, Mercury, Venus, Mars) are taken to describe day-to-day compatibility; those between social and generational planets (Jupiter and beyond) point to deeper, longer-term themes.

There is no such thing as a "bad" aspect Couples who see squares and oppositions in synastry often ask whether their charts are "incompatible". The traditional view rejects the question: tense aspects do not make a relationship easy, but they show what the relationship grows through. A synastry made only of trines and sextiles is, ironically, often described as dull — growth needs friction.

Synastry is not the same as composite

Synastry compares two charts — they remain two separate people's charts. A composite chart instead derives a mathematical third chart from the midpoints between them, and treats the relationship as a single "personality". Synastry is closer to "how do we treat each other"; composite is closer to "what are we together".

Natal Chart

The single-person chart synastry is built from.

Composite Chart

The third chart, cast for the relationship itself.

ALVEM's Synastry screen overlays the two charts and lists both the planet-to-planet and the planet-to-house comparisons.