What Is Synastry?
Synastry is the branch of astrology that examines relationships by overlaying two birth charts and analyzing the aspects (angular relationships) formed between the planets of one person's chart and those of another's. Where one person's planet falls in the other's chart, and what planets connect between the two charts, reveals the energetic dynamic between them: what attracts, what challenges, what supports, and what transforms.
The Most Significant Synastry Aspects
Sun conjunct Sun: Strong identity resonance — similar values and self-expression. Natural affinity and mutual recognition. Sun conjunct Moon: One of the most significant connection aspects — deep emotional compatibility and mutual support. Often found in long-term partnerships. Venus conjunct Mars: The classic sexual attraction aspect — physical chemistry and romantic excitement. Moon conjunct Moon: Emotional mirroring — you understand each other's emotional world instinctively. Deeply comfortable.
The Challenging but Powerful Aspects
Saturn conjunct personal planets: Saturn aspects in synastry create lasting bonds through commitment, responsibility, and karmic lessons. Can feel restrictive or heavy, but provide structure and longevity. Many long-term marriages have prominent Saturn contacts. Pluto conjunct personal planets: Intense, transformative, and sometimes overwhelming. These connections change both people fundamentally — for better or worse, depending on the individuals.
Venus and Mars: The Attraction Signature
Venus-Mars aspects between charts create the fundamental romantic/sexual energy of a relationship. Venus conjunct or trine Mars is magnetic and harmonious; Venus square Mars creates tension alongside attraction; Venus opposite Mars is highly charged — attraction through difference. The Venus-Mars interaspect essentially determines the quality of physical and romantic energy between two people.
Composite Charts
Beyond synastry (two charts overlaid), composite charts are calculated by finding the midpoint between each pair of planets to create a third chart representing the relationship itself as an entity. The composite Sun sign reveals the relationship's core nature and purpose; the composite Venus and Mars show its romantic and physical energy; the composite Saturn shows where the relationship must work and grow. Composite charts are invaluable for understanding the deeper purpose and direction of a significant relationship.