---
title: "Coalescent Chart"
method: POST
path: "/coalescent"
tags: ["Comparisons"]
---

# Coalescent Chart

`POST /coalescent`

Calculate a coalescent chart — the harmonic chart that resonates most strongly between two charts.

## Request body

- Coalescent
  - `input1` ChartInput, required — Birth data for a single natal chart. Required: date (YYYY-MM-DD), time (HH:mm:ss). Coordinates are latitude and longitude in decimal degrees, plus timezoneOffset in hours from UTC; the short forms lat, lon, lng and tz are rejected with 400 INVALID_FIELD. Omitting the coordinates is not the same as skipping them: houses, angles and everything derived from them are then computed for 0°N 0°E at UTC, which is a wrong answer rather than a neutral default.
    - `date` string, required
    - `time` string, required
    - `timezoneOffset` number, nullable
    - `latitude` number, nullable
    - `longitude` number, nullable
    - `houseSystem` string
    - `name` string
    - `city` string
    - `zodiacType` 'tropical' | 'sidereal'
    - `ayanamsaId` number, nullable
    - `cosmogram` boolean
  - `input2` ChartInput, required — Birth data for a single natal chart. Required: date (YYYY-MM-DD), time (HH:mm:ss). Coordinates are latitude and longitude in decimal degrees, plus timezoneOffset in hours from UTC; the short forms lat, lon, lng and tz are rejected with 400 INVALID_FIELD. Omitting the coordinates is not the same as skipping them: houses, angles and everything derived from them are then computed for 0°N 0°E at UTC, which is a wrong answer rather than a neutral default.
    - `date` string, required
    - `time` string, required
    - `timezoneOffset` number, nullable
    - `latitude` number, nullable
    - `longitude` number, nullable
    - `houseSystem` string
    - `name` string
    - `city` string
    - `zodiacType` 'tropical' | 'sidereal'
    - `ayanamsaId` number, nullable
    - `cosmogram` boolean

## Response `200`

Successful calculation

- object
  - `ok` boolean
  - `data` object
    - `harmonic` number, nullable
    - `planets` unknown[], nullable
      - unknown
    - `houses` object, nullable
      - `ascendant` number, nullable
      - `cusps` unknown[], nullable
        - unknown
    - `aspects` unknown[], nullable
      - unknown
    - `resonance` number, nullable

## Other responses

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

---

[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/793e5c2dbcdf/schema)