Compute synastry, composite, and Davison relationship charts between two people.

Compare Two Charts

The Morphemeris API offers three approaches to relationship chart analysis. Each answers a different question about how two people relate to each other.

Synastry: how do they affect each other?

Synastry computes both natal charts and finds the inter-chart aspects — how person A's planets interact with person B's planets.

Bash

curl "https://api.morphemeris.com/v1/synastry?\
datetime_a=1990-06-15T18:30:00Z&lat_a=40.7128&lon_a=-74.006\
&datetime_b=1988-03-22T10:00:00Z&lat_b=51.5074&lon_b=-0.1278\
&applying=true" \
  -H "Authorization: Bearer morphemeris_live_YOUR_KEY"

javascript

const params = new URLSearchParams({
  datetime_a: "1990-06-15T18:30:00Z", lat_a: "40.7128", lon_a: "-74.006",
  datetime_b: "1988-03-22T10:00:00Z", lat_b: "51.5074", lon_b: "-0.1278",
  applying: "true",
});
const res = await fetch(
  `https://api.morphemeris.com/v1/synastry?${params}`,
  { headers: { Authorization: "Bearer morphemeris_live_YOUR_KEY" } }
);
const { data } = await res.json();

// Both full charts
console.log("Person A's Sun:", data.chart_a.bodies.find(b => b.name === "sun"));
console.log("Person B's Sun:", data.chart_b.bodies.find(b => b.name === "sun"));

// Inter-chart aspects
for (const asp of data.inter_aspects) {
  console.log(`A's ${asp.body_a} ${asp.aspect} B's ${asp.body_b} (orb: ${asp.orb.toFixed(2)}°)`);
}

Python

import requests

res = requests.get(
    "https://api.morphemeris.com/v1/synastry",
    params={
        "datetime_a": "1990-06-15T18:30:00Z", "lat_a": 40.7128, "lon_a": -74.006,
        "datetime_b": "1988-03-22T10:00:00Z", "lat_b": 51.5074, "lon_b": -0.1278,
        "applying": "true",
    },
    headers={"Authorization": "Bearer morphemeris_live_YOUR_KEY"},
)
data = res.json()["data"]

for asp in data["inter_aspects"]:
    print(f"A's {asp['body_a']} {asp['aspect']} B's {asp['body_b']} (orb: {asp['orb']:.2f}°)")

The response includes chart_a, chart_b (full natal charts), and inter_aspects (aspects between the two charts).

Composite: what is the relationship?

A composite chart merges two charts into one by averaging corresponding positions. It represents the relationship itself as an entity.

Bash

curl "https://api.morphemeris.com/v1/composite?\
datetime_a=1990-06-15T18:30:00Z&lat_a=40.7128&lon_a=-74.006\
&datetime_b=1988-03-22T10:00:00Z&lat_b=51.5074&lon_b=-0.1278" \
  -H "Authorization: Bearer morphemeris_live_YOUR_KEY"

The response is a single chart (same structure as /v1/natal-chart) with metadata.source set to "composite".

Davison: the relationship as a real chart

The Davison chart finds the midpoint in time and space between two births and casts a real chart for that moment and place.

Bash

curl "https://api.morphemeris.com/v1/davison?\
datetime_a=1990-06-15T18:30:00Z&lat_a=40.7128&lon_a=-74.006\
&datetime_b=1988-03-22T10:00:00Z&lat_b=51.5074&lon_b=-0.1278" \
  -H "Authorization: Bearer morphemeris_live_YOUR_KEY"

Check metadata.datetime and metadata.lat/metadata.lon to see the computed midpoint.

All three in one batch

Get all three relationship charts in a single API call:

JSON

{
  "requests": [
    {
      "endpoint": "/v1/synastry",
      "params": {
        "datetime_a": "1990-06-15T18:30:00Z", "lat_a": 40.7128, "lon_a": -74.006,
        "datetime_b": "1988-03-22T10:00:00Z", "lat_b": 51.5074, "lon_b": -0.1278
      }
    },
    {
      "endpoint": "/v1/composite",
      "params": {
        "datetime_a": "1990-06-15T18:30:00Z", "lat_a": 40.7128, "lon_a": -74.006,
        "datetime_b": "1988-03-22T10:00:00Z", "lat_b": 51.5074, "lon_b": -0.1278
      }
    },
    {
      "endpoint": "/v1/davison",
      "params": {
        "datetime_a": "1990-06-15T18:30:00Z", "lat_a": 40.7128, "lon_a": -74.006,
        "datetime_b": "1988-03-22T10:00:00Z", "lat_b": 51.5074, "lon_b": -0.1278
      }
    }
  ]
}

This costs 9 credits (3 per chart) and returns all three relationship charts in a single round trip.

Tips

Synastry is the most commonly used technique — start here for relationship analysis.
Composite is best for understanding the relationship's themes and dynamics.
Davison is best when you need to time events — transits to the Davison chart indicate when things happen in the relationship.
All three endpoints use _a / _b suffixed parameters. The order doesn't affect aspects (Sun A trine Venus B is the same relationship regardless of which person is A).
See Concepts: Relationship Charts for a deeper comparison of the three approaches.

Compare Two Charts (Synastry)

Compare Two Charts

Synastry: how do they affect each other?

Composite: what is the relationship?

Davison: the relationship as a real chart

All three in one batch

Tips

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