A plain-language definition for anyone researching synastry, what it is, where it comes from, and how practitioners use it.
85 plain-language definitions · Cited sources · Persona-authored
By Astrid Moon · Updated August 3, 2026
Resident Astrologer
What is synastry?
Synastry is the astrological technique of comparing two natal charts to study the relationship between them. In traditional Western astrology, the aspects between one person's planets and the other's are read as the chemistry, friction, and growth edges of the partnership.
Synastry overlays one chart on top of another, treating each person's planets as transits to the partner's chart. The chart suggests where two people will instinctively meet, where they will misunderstand each other, and which life domains the relationship is here to develop, what astrologer Liz Greene calls the 'meeting field' between two psyches.
In traditional Western astrology, synastry is not a compatibility score. The chart suggests qualities, not verdicts. Two people with many squares between them can build something more durable than two with only trines, because the squares describe the growth edges, and growth is often what relationships are for.
Synastry has roots in Hellenistic astrology, where chart comparison was used to evaluate political alliances, business partnerships, and marriages. The modern psychological approach to synastry was developed in the 20th century by astrologers including Liz Greene, Stephen Arroyo, and Robert Hand, who reframed it as a tool for understanding relational patterns rather than predicting outcomes. According to Hand, the most useful synastry reading examines both charts as if they were one larger system.
A full synastry reading typically examines: Sun-Moon contacts (emotional resonance), Venus-Mars contacts (attraction and desire), Saturn contacts (commitment and weight), and the houses each person's planets fall into within the partner's chart. Free synastry charts can generate the overlay automatically.
Astrologers usually look first at the inner-planet contacts (Moon through Mars), since these describe day-to-day relating. Outer-planet contacts (Saturn through Pluto) describe the deeper, slower-moving themes, the parts of the relationship that change you. The chart suggests reading both layers, not just one.
These glossary terms are closely connected to synastry:
Synastry compares two separate charts; a composite chart merges them into one new chart representing the relationship itself. Most astrologers read both for a complete picture.
Sun and Moon contacts describe core resonance. Venus and Mars describe attraction. Saturn describes commitment. Each layer reveals a different facet of the relationship.
No. In tradition, synastry describes the dynamics and growth edges of a connection, but human choice and circumstance are not in the chart.
Yes, especially for any reading that involves houses or the Moon's exact degree. A daily-resolution chart can still show planet-to-planet aspects but loses the house overlay.
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