Swiss Ephemeris API

What computes the positions

Asterwise uses the Swiss Ephemeris for planetary positions and house calculations, and accepts dates from 1800 through 2099. Between 1950 and 2050 the published check against NASA JPL Horizons shows a median difference of 0.046 arcseconds. You do not install a library, compile bindings or ship ephemeris files; you send JSON and get JSON back.

Tropical or sidereal

Every birth request accepts an ayanamsa field: lahiri (default), raman, kp, or tropical for zero offset. Western endpoints under /v1/western/ are always tropical. Details in the ayanamsa reference.

Request: a Western natal chart

curl -X POST https://api.asterwise.com/v1/western/natal \
  -H "Authorization: Bearer $ASTERWISE_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"date":"1985-11-12","time":"06:45","latitude":19.076,"longitude":72.8777,"timezone":"Asia/Kolkata","house_system":"placidus"}'

House systems: placidus (default), koch, equal, whole_sign.

Response, abbreviated

{
  "success": true,
  "data": {
    "zodiac": "tropical",
    "house_system": "placidus",
    "ascendant": { "longitude": 228.957682, "sign": "Scorpio", "degree_in_sign": 18.957682 },
    "mc":        { "longitude": 140.343251, "sign": "Leo", "degree_in_sign": 20.343251 },
    "planets": [
      { "name": "Sun",  "longitude": 229.596712, "sign": "Scorpio", "house": 1,  "is_retrograde": false, "dignity": "peregrine" },
      { "name": "Moon", "longitude": 221.838294, "sign": "Scorpio", "house": 12, "is_retrograde": false, "dignity": "fall" }
    ],
    "aspects": [ { "planet_a": "Jupiter", "planet_b": "Mars", "type": "trine", "exact_angle": 119.9635, "orb": 0.0365, "is_applying": false } ],
    "elements": { "fire": 2, "earth": 1, "air": 2, "water": 5, "dominant": "water" }
  }
}

Ten planets Sun through Pluto with sign, degree, house, retrograde flag and essential dignity; house cusps; all active aspects with orb; element, modality and hemisphere counts. Field list in the Western natal chart reference. The sidereal equivalent is POST /v1/astro/natal.

How accurate, measured

80 apparent geocentric longitudes (10 bodies at 8 instants between 1950 and 2050) were computed by this engine and by NASA JPL Horizons, which shares no code with the Swiss Ephemeris. Median difference 0.046 arcseconds, 95th percentile 0.232 arcseconds, 79 of 80 within half an arcsecond. The raw JSON and the comparison script are on the accuracy page; the reference chart with every planet next to an independent Swiss Ephemeris run is on the proof page.

Beyond positions

The same engine feeds 118 endpoints: Vedic natal and divisional charts, dasha, matchmaking, panchanga, transits, returns, progressions, synastry and composite charts. Rate limits per plan are in the rate limits reference.