Synastry is the astrological technique of comparing two natal charts to reveal relationship dynamics and potential. The reading analyzes inter-planetary aspects between the two charts — attractions, tensions, karmic connections and evolutionary potentials. Special emphasis is placed on aspects between the Sun, Moon, Venus, Mars and Ascendant of both partners. The result reveals relationship strengths and weaknesses and provides concrete guidelines for harmonious partnership.
Where it comes from
Comparing two birth charts is as old as the natal chart itself. Hellenistic and medieval astrologers wrote on marriage compatibility, and the Arabic tradition developed detailed rules for it. The modern form, which overlays one chart on the other and reads the contacts between them, took shape in the twentieth century. The composite chart, which averages two charts into a third, is a separate and more recent technique, developed in the 1970s.
How the method works
Synastry places one person's planets against the other's chart and reads the aspects between them. Sun to Moon contacts are read for basic compatibility of temperament; Venus to Mars for attraction; Moon to Moon for emotional rhythm; Saturn contacts for durability and for weight. Which house one person's planet falls into in the other's chart says which area of life they affect. Hard aspects — squares and oppositions — are not read as failure but as the places where the relationship generates heat, and long relationships usually have several.
What a reading covers
A reading gives the strongest contacts between the two charts, what each contributes, where the friction sits and what form it takes, the houses activated in each direction, and what the relationship tends to ask of each person.
Common questions
- Do we both need exact birth times?
- For the house overlays and the angles, yes. Without them the planet-to-planet aspects still work, which is a large part of the reading but not the most specific part.
- Are hard aspects a reason to worry?
- No. Charts with no hard contacts are often read as lacking charge. What matters is which planets make them — Saturn to Moon is a different problem from Mars to Mars.
- Is synastry the same as a composite chart?
- No. Synastry compares two charts and reads the contacts. A composite merges them into a single chart read as the relationship itself. They answer different questions and are often used together.