Synastry Chart — Compare Two Birth Charts

A synastry chart compares two birth charts to reveal the astrological dynamics between two people. Instead of one chart, you overlay both — placing one person’s planets against the other’s — and read the angles (aspects) that form between them. Those aspects describe how you actually meet: where there’s ease and attraction, and where there’s tension to work through.

Sigastra computes each chart from the real positions of the Sun, Moon and planets with the Swiss Ephemeris, using each person’s exact birth date, time and place. The bi-wheel above is your live chart — Person A on the inner ring, Person B on the outer — with every inter-chart aspect drawn across the centre.

The most telling contacts are between the personal points. Sun–Moon aspects show how your core selves and emotional needs fit; Venus–Mars is the classic chemistry axis; Moon–Moon and Moon–Venus speak to emotional comfort and affection. Aspects to the Ascendant add instant recognition and physical attraction.

Harmonious aspects (trine, sextile, and many conjunctions) flow easily; hard aspects (square, opposition) create friction that can be either growth or grind. The synastry score above weighs the luminaries and tighter orbs most heavily, so it reflects the relationship’s overall grain — not a verdict.

Synastry looks at two charts in dialogue — your planets touching theirs. A composite chart is different: it’s a single new chart built from the midpoints of both people’s placements, describing the relationship as its own entity, with its own Sun, Moon and Ascendant.

Both are worth reading together. Synastry tells you how you affect each other; the composite tells you what the relationship itself is like. Pro generates the composite chart alongside the interpretation, so you get both views.

The calculator here is genuinely free: enter both charts and you get the real bi-wheel, every inter-chart aspect, the harmonious/challenging balance and the synastry score — computed, not guessed, and yours to explore as many times as you like.

Pro adds the interpretation layer: an aspect-by-aspect written reading across overview, emotional bond, communication, attraction, friction and long-term potential, plus the composite chart, saving, and PDF export. It’s the difference between the data and the story.

The Moon and the Ascendant move fast — the Moon changes sign roughly every 2.5 days and the Ascendant every ~2 hours — so an accurate birth time sharpens the most relationship-relevant points. If a time is genuinely unknown you can still run the chart (we default to noon), but the Moon and angles may shift.

For your own precise placements, calculate your full birth chart first — it computes your exact Sun, Moon and Rising from the real sky at your moment of birth.