Compatibility is not a ranking
Sun-sign compatibility lists are entertaining, but they reduce two complex people to one placement each. Synastry compares the relationships between two complete natal charts. Even then, it describes symbolic dynamics rather than determining whether a relationship is healthy, lasting or right.
No chart pairing overrides communication, consent, shared values, safety or observed behavior.
What astrologers compare
Common starting points include contacts between the Sun, Moon, Mercury, Venus and Mars; connections to the Ascendant and Midheaven; Saturn contacts associated with structure and responsibility; and the houses activated in each person's chart. Aspects describe the angular relationship between planets and may suggest ease, stimulation, friction or a repeated learning pattern.
Easy is not always better
Harmonious aspects can support familiarity and flow, but too much ease may also allow avoidance. Challenging aspects can produce conflict, attraction, growth or exhaustion depending on maturity and context. A square is not a command to separate, and a trine is not a promise of happiness.
Birth-time uncertainty matters twice
When either birth time is unknown, the Ascendant, houses and angle contacts may be unreliable. A responsible comparison can still examine planetary sign positions and aspects that remain stable, while clearly omitting uncertain factors. Fabricated precision is especially misleading in relationship questions because people may make emotional decisions from it.
Questions that create value
Ask how each person communicates under stress, seeks reassurance, handles desire, sets boundaries and carries responsibility. Then compare the symbolism with lived experience. The chart can provide language for a conversation; the relationship itself provides the evidence.
For decisions involving abuse, coercion, mental health, money or legal rights, seek qualified help rather than relying on compatibility astrology.