---
title: "Synastry"
method: POST
path: "/synastry"
tags: ["Comparisons"]
---

# Synastry

`POST /synastry`

Calculate cross-chart aspects between two natal charts for relationship analysis. Either partner may set timeUnknown: true: cross-aspects are still returned, while that partner's houses, angles and sect come back null.

## Request body

- TwoChartUnknownTime — Pair of natal charts where either birth time may be unknown. A chart with timeUnknown: true contributes planets and cross-aspects but no houses, angles or overlays.
  - `chart1` ChartInputUnknownTime, required — Birth data where the clock time may be unknown. Either pass time (HH:mm:ss), or set timeUnknown: true and omit it. In the second case the response carries planets and aspects but no houses, angles or sect.
    - `date` string, required
    - `time` string
    - `timezoneOffset` number, nullable — Hours from UTC at the given moment, not minutes. Fractional zones are hours too: 5.5 for India, 5.75 for Nepal, -3.5 for Newfoundland. Defaults to 0, meaning UTC.
    - `latitude` number, required
    - `longitude` number, required
    - `houseSystem` string
    - `name` string
    - `city` string
    - `zodiacType` 'tropical' | 'sidereal'
    - `ayanamsaId` number, nullable
    - `ayanamsa` 'fagan-bradley' | 'lahiri' | 'de-luce' | 'raman' | 'krishnamurti' | 'kp' | 'yukteshwar' | 'jn-bhasin' | 'true-citra' | 'djwhal-khul' — Sidereal school by name. Lahiri when omitted. Equivalent to ayanamsaId; send either.
    - `cosmogram` boolean
    - `timeUnknown` boolean
  - `chart2` ChartInputUnknownTime, required — Birth data where the clock time may be unknown. Either pass time (HH:mm:ss), or set timeUnknown: true and omit it. In the second case the response carries planets and aspects but no houses, angles or sect.
    - `date` string, required
    - `time` string
    - `timezoneOffset` number, nullable — Hours from UTC at the given moment, not minutes. Fractional zones are hours too: 5.5 for India, 5.75 for Nepal, -3.5 for Newfoundland. Defaults to 0, meaning UTC.
    - `latitude` number, required
    - `longitude` number, required
    - `houseSystem` string
    - `name` string
    - `city` string
    - `zodiacType` 'tropical' | 'sidereal'
    - `ayanamsaId` number, nullable
    - `ayanamsa` 'fagan-bradley' | 'lahiri' | 'de-luce' | 'raman' | 'krishnamurti' | 'kp' | 'yukteshwar' | 'jn-bhasin' | 'true-citra' | 'djwhal-khul' — Sidereal school by name. Lahiri when omitted. Equivalent to ayanamsaId; send either.
    - `cosmogram` boolean
    - `timeUnknown` boolean

## Response `200`

Successful calculation

- object
  - `ok` boolean
  - `data` object
    - `aspects` object[], nullable
      - `body1` number, nullable
      - `body2` number, nullable
      - `chart1Planet` string, nullable
      - `chart2Planet` string, nullable
      - `type` string, nullable
      - `orb` number, nullable
      - `applying` boolean, nullable

## Other responses

- `400` — Validation error
- `401` — Missing or invalid API key

## Changes

- **2026-08-18** `dd3764875e7a` — 2 info
  - added the new optional request property `chart1/ayanamsa`
  - added the new optional request property `chart2/ayanamsa`
- **2026-08-15** `e637d1a9911b` — 4 warning
  - the `chart1/timezoneOffset` request property's max was set to `14.00`
  - the `chart2/timezoneOffset` request property's max was set to `14.00`
  - the `chart1/timezoneOffset` request property's min was set to `-14.00`
  - the `chart2/timezoneOffset` request property's min was set to `-14.00`
- **2026-08-11** `b0533bcc12c0` — 8 breaking, 8 warning, 4 info
  - the request property `chart1/latitude` became not nullable
  - the request property `chart1/longitude` became not nullable
  - the request property `chart2/latitude` became not nullable
  - the request property `chart2/longitude` became not nullable
  - …16 more

[Change history](https://skmtc.dev/astroway/apis/astroway-calculation-api/changes/synastry/post.md)

---

[API](https://skmtc.dev/astroway/apis/astroway-calculation-api.md) · [All operations](https://skmtc.dev/astroway/apis/astroway-calculation-api/llms.txt) · [OpenAPI document](https://skmtc-service-production.skmtc.workers.dev/v1/apis/astroway/astroway-calculation-api/revisions/dd3764875e7a/schema)