Two-chart relationship astrology
Synastry Aspects: How Two Charts Interact
Synastry compares one person's planets with the other person's. A contact such as Venus square Mars or Moon conjunct Moon describes one specific interaction between two charts, not a complete relationship verdict and not a single-person placement.
The guides below explain the mechanism of a cross-chart contact. Use the calculator first to see which contacts, house overlays and angle connections are actually present for both people.
Editorial review by Luis PhamMethodology
What synastry measures
Planetary functions
Identity, emotion, affection, pursuit, thought, growth and boundaries meet through specific planet-to-planet contacts.
Aspect geometry
The engine reports the measured separation, the canonical angle and the resulting orb. A conjunction is centred on 0°, a square on 90° and an opposition on 180°; the geometry describes a relationship between points, not a verdict.
Chart context
Signs and cross-aspects use planetary positions. Each house overlay is directional: A's planet in B's house is separate from B's planet in A's house. Houses and angles require the receiving chart's recorded time.
What birth-time certainty changes
A real comparison should preserve uncertainty instead of filling in a missing time. The engine keeps planet-to-planet contacts available while narrowing the claims that depend on houses, angles or a time-sensitive Moon.
Both times known
Cross-aspects, both overlay directions and angle contacts can be calculated under the declared house system.
A known · B unknown
A-to-B overlays and B's angles are unavailable; planet positions remain available, with B time-dependent results withheld.
A unknown · B known
B-to-A overlays and A's angles are unavailable; the reverse direction is kept distinct rather than guessed.
Both unknown
Use the planet contacts that the dates support. Houses and angles stay out, and a fast Moon may be possible or unavailable.
A practical order for comparing two charts
Use the comparison as a sequence of questions. This keeps one dramatic contact from standing in for the whole relationship.
1. Calculate both charts
Start with the actual planet positions. If a birth time is missing, time-dependent houses and angles stay out.
2. Find the contacts
Notice the cross-chart aspects and their orbs before choosing a story about attraction, emotion or conflict.
3. Add overlays
When the inputs support it, inspect house overlays and angle contacts to see where the interaction lands in each chart.
4. Ask a bounded question
Use the evidence to explore a specific pattern. Synastry can describe dynamics; it cannot guarantee an outcome.
Read synastry by relationship question
These are curated entry points into the authored aspect library. The complete comparison remains the source of truth for a real pair.
Emotional and attachment contacts
Read these contacts when the main question is emotional recognition, safety, responsiveness or the way care gets exchanged.
- Sun Conjunct Moon in SynastrySun Conjunct Moon in synastry: measured cross-chart geometry, orb, role-specific dynamics and house-overlay context.
- Sun Square Moon in SynastrySun Square Moon in synastry: measured cross-chart geometry, orb, role-specific dynamics and house-overlay context.
- Moon Conjunct Venus in SynastryMoon Conjunct Venus in synastry: measured cross-chart geometry, orb, role-specific dynamics and house-overlay context.
Attraction and pursuit contacts
These pages focus on desire, receptivity, initiative and the loop that can turn chemistry into cooperation or friction.
- Venus Conjunct Mars in SynastryVenus Conjunct Mars in synastry: measured cross-chart geometry, orb, role-specific dynamics and house-overlay context.
- Venus Square Saturn in SynastryVenus Square Saturn in synastry: measured cross-chart geometry, orb, role-specific dynamics and house-overlay context.
- Venus Opposite Pluto in SynastryVenus Opposite Pluto in synastry: measured cross-chart geometry, orb, role-specific dynamics and house-overlay context.
Identity, direction and influence
These contacts describe how confidence, purpose, growth, action or standards become activated between two charts.
- Mars Square Pluto in SynastryMars Square Pluto in synastry: measured cross-chart geometry, orb, role-specific dynamics and house-overlay context.
- Sun Conjunct Mars in SynastrySun Conjunct Mars in synastry: measured cross-chart geometry, orb, role-specific dynamics and house-overlay context.
- Sun Conjunct Jupiter in SynastrySun Conjunct Jupiter in synastry: measured cross-chart geometry, orb, role-specific dynamics and house-overlay context.
Communication and meaning-making
Use this group for contacts where thought, language, interpretation and shared mental rhythm are the central relationship question.
Mirrored planetary contacts
Same-planet contacts are read as shared rhythm rather than assigning one fixed role to each person.
- Moon Conjunct Moon in SynastryMoon Conjunct Moon in synastry: measured cross-chart geometry, orb, role-specific dynamics and house-overlay context.
- Mars Conjunct Mars in SynastryMars Conjunct Mars in synastry: measured cross-chart geometry, orb, role-specific dynamics and house-overlay context.
- Venus Conjunct Venus in SynastryVenus Conjunct Venus in synastry: measured cross-chart geometry, orb, role-specific dynamics and house-overlay context.
How to read one contact
Start with the two planetary functions. Check the canonical angle against the measured separation and orb, then inspect the directional overlays, birth-time state and wider contacts before generalising.
Synastry is not Sun-sign compatibility
Sun-sign pair pages describe a broad sign-level interaction. Synastry uses both complete charts to measure actual contacts. The two lenses answer different questions and should not be merged into one score.
Synastry, natal and composite answer different questions
A natal chart describes one person. Synastry compares A's points with B's points. A composite chart creates a separate midpoint chart for the relationship and should not be used to rewrite a cross-chart orb or overlay. This hub covers synastry; the calculator is the private source of truth for a real pair.
Compare both birth charts
Calculate the real planetary contacts, house overlays and angle connections between two people. If a birth time is unknown, time-dependent results stay omitted rather than guessed.
Open the compatibility calculator