Synastry API

The synastry endpoint computes both natal charts independently, then overlays them to find inter-chart aspects: every angular relationship where a planet in chart A meets a planet in chart B within orb. Each cross-aspect is returned with both bodies named, the aspect type (conjunction, sextile, square, trine, opposition and the minor angles), the exact orb, and the direction of contact so you know whose Venus is trining whose Mars. The full planet sets for both subjects come back alongside, so you can render a bi-wheel or feed a compatibility scorer without a second round-trip.

curl -X POST https://api.astroway.info/v1/synastry \
  -H "X-Api-Key: aw_live_..." \
  -H "Content-Type: application/json" \
  -d '{
    "chart1": { "date": "1990-05-15", "time": "14:30:00", "timezoneOffset": 3, "latitude": 50.45, "longitude": 30.52 },
    "chart2": { "date": "1985-11-03", "time": "08:15:00", "timezoneOffset": 2, "latitude": 48.46, "longitude": 35.04 }
  }'

{
  "ok": true,
  "data": {
    "crossAspects": [
      { "planet1": "Venus", "planet2": "Mars", "type": "trine", "orb": 0.8, "direction": "A→B" }
    ],
    "chart1": { "input": { ... }, "planets": [ ... ] },
    "chart2": { "input": { ... }, "planets": [ ... ] }
  }
}

This is the backbone endpoint for dating and matchmaking apps, relationship-report products, and any feature that answers "how do these two people relate?". Pair it with our compatibility-scoring helper to turn the raw cross-aspects into a single percentage, or pass the grid to an LLM for a written relationship reading. Because both charts are returned in full, one synastry call replaces three (two natal charts plus the overlay) — compute it once and cache the result keyed on the two birth moments. Method follows Robert Hand and Stephen Arroyo; the composite and Davison midpoint techniques live on their own endpoints when you need a single merged chart instead of an overlay.

Cross-aspects use the same orb policy as the natal aspect grid. Both subjects accept the full /v1/chart parameter set, including per-subject house system and timezone offset. Synastry is a Tier 3 endpoint (two charts + an overlay scan); cache aggressively since the result is fully deterministic for a given pair of birth moments.