How synastry works
Each of you has a birth chart, a snapshot of where the planets were when you were born. Synastry lays one chart over the other and asks two questions. First, how do the planets meet? When your Venus sits in a trine to their Mars, or your Moon is conjunct their Sun, astrologers read a specific kind of connection between those parts of your personalities. Second, where do the planets land? Your partner's Venus falling in your 7th house of partnership, or their Saturn in your 4th house of home, colours how that relationship feels in daily life.
The bi-wheel shows both at once. The inner ring is Person 1's chart with their houses; the outer ring holds Person 2's planets. The lines in the centre are the aspects between the two charts: blue for flowing, red for challenging, gold for conjunctions.
Reading the connections
| Contact | Traditionally read as |
|---|---|
| Sun and Moon | Deep compatibility of identity and needs, the classic marriage aspect |
| Venus and Mars | Attraction and chemistry |
| Moon and Moon | Emotional rhythm, how easy it is to live together |
| Mercury and Mercury | How you talk, argue and make plans |
| Saturn to personal planets | Commitment, duty and tests of patience |
| Rising sign contacts | Instant recognition and physical ease together |
Flowing aspects (trines and sextiles) are read as ease; challenging ones (squares and oppositions) as friction that can create both tension and spark. Most lasting relationships have both. A chart full of trines can feel pleasant but low in energy; a few squares are often what keeps things interesting.
House overlays
When both birth times are known, the calculator lists where each person's planets fall in the other's houses. If their Sun lands in your 10th house, astrologers say they light up your career or public life; their Moon in your 4th house suggests they feel like home. These overlays are only as accurate as the birth times, so treat them as a guide when a time is approximate.
A note on compatibility
Synastry describes a relationship's textures, not its fate. No combination of aspects guarantees success or dooms a couple, and the calculator does not reduce two people to a percentage. Use it as a way to talk about differences and strengths. For a different angle on the same question, add your partner to the astrocartography map and find the places that suit you both.