ASTROLOGICAL FILES
Synastry compatibility
WHAT'S YOUR SIGN?
Synastry compares two natal charts to study how one person's planets and angles relate to the other person's chart. It can describe ease, friction, attraction, recognition, responsibility, and recurring translation work. It cannot certify that a relationship is safe, permanent, mutual, or destined.
A careful reading moves from accurate birth data to repeated patterns. It does not rank a couple from one Sun-sign pairing or isolate one dramatic aspect. Use this hub to understand the method, decide what can be calculated with the data available, and follow focused guides without losing the whole relationship context.
LL-AST-046 / updated 23.08.26
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01
How two charts are compared
Each natal chart is calculated independently before comparison. Synastry then measures angular distances between planets and points across the two charts. A conjunction brings functions into the same degree area; an opposition places them across an axis; squares emphasize friction and action; trines and sextiles can describe fluency or available cooperation. The aspect's orb shows how close it is to exact.
The same aspect changes with the planets involved. A Moon-Saturn contact is not interpreted like a Venus-Mars contact, even when both are squares. Sign, house, natal condition, angle involvement, and repeated themes matter. The practical question is not whether an aspect is good, but what it asks the two people to notice, translate, practice, or protect.
02
Personal planets and everyday compatibility
The Sun concerns direction and vitality; the Moon concerns needs and familiar emotional rhythm; Mercury concerns perception and communication; Venus concerns value, affection, and attraction; Mars concerns desire, assertion, and conflict. Contacts among these planets often describe the parts of a relationship that are felt most frequently in ordinary life.
A flowing aspect may make a style feel immediately understandable, but ease can become assumption. A hard aspect can create conflict, fascination, or productive difference depending on maturity and context. Look for mutual responsiveness and observable repair instead of translating intensity into proof that the relationship must continue.
03
House overlays and angles
When both birth times are reliable, each person's planets can be placed in the other person's houses. A planet falling near the Ascendant, Descendant, Midheaven, or Imum Coeli can feel especially visible. House overlays describe where a person activates another chart: identity, resources, communication, home, creativity, partnership, intimacy, vocation, or another field of life.
House overlays depend on time and place. If either time is unknown, Lunar Letter removes those claims rather than using a noon chart as exact. Even with accurate data, a house overlay does not reveal intent. It identifies a symbolic area of activation that should be compared with the lived relationship.
04
Saturn, Pluto, Nodes, and Chiron
Saturn contacts can emphasize duration, accountability, fear, structure, delay, or the work required to make trust durable. Pluto contacts can intensify questions of power, exposure, compulsion, and transformation. Neither planet proves longevity or abuse; both require careful attention to boundaries, consent, and actual conduct.
Nodes and Chiron are often described with fated language, but that language can overstate what a chart shows. Nodal contacts can mark a strong sense of direction or familiarity. Chiron contacts can highlight sensitivity, care, defensiveness, or learning around an old wound. A responsible reading keeps these symbols proportionate and avoids using them to excuse harm.
05
Unknown birth time
Without a reliable birth time, many planetary sign positions and interplanetary aspects remain usable. The Sun, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto generally move slowly enough for a date-based comparison, although exact degrees still need an internally consistent assumed time for computation. The Moon can move far enough in one day to require a range.
Houses, Ascendant, Midheaven, Vertex, and angle contacts should be omitted. The result should state what remains valid and what has been removed. This is more useful than either refusing all comparison or presenting unsupported precision. See the focused unknown-time guide before entering approximate data.
06
Synastry versus composite charts
Synastry keeps two natal charts intact and studies their interaction. A composite chart creates one symbolic chart from the midpoints between corresponding planets and angles. Synastry asks how two people affect each other; a composite reading asks how the relationship behaves as a shared system. They answer related but different questions.
Use synastry first when the concern is communication, attraction, emotional safety, or a recurring interpersonal trigger. Add a composite chart when the relationship itself has a recognizable identity, public role, rhythm, or developmental task. Neither technique replaces the natal charts or the evidence available in the relationship.
07
Limits of compatibility scoring
A single score hides method choices: which points were included, how aspects were weighted, what orbs were allowed, and whether unknown birth times were treated honestly. Two charts can contain both effortless rapport and serious pressure. A useful interpretation names those different layers rather than collapsing them into a percentage.
Compatibility also includes factors no chart can verify: consent, accountability, practical availability, shared values, safety, and willingness to repair. Treat the chart as a map for better questions. Let behavior answer whether the relationship can hold what the symbols describe.
QUESTIONS
Questions about this subject
What does a synastry calculator compare?
It compares planetary degrees between two natal charts and, when birth times are known, house overlays and angle contacts.
Can I calculate synastry without a birth time?
Yes, with limits. Many planet-to-planet aspects remain available, while houses, angles, and some Moon precision must be removed or qualified.
Is synastry the same as a composite chart?
No. Synastry compares two separate charts. A composite chart creates one midpoint chart for the relationship as a symbolic unit.
Can synastry tell me what another person feels?
No. It can describe relationship patterns and possible sensitivities, but feelings and intentions require direct evidence and communication.