@fusionstrings/swisseph-wasi

Swiss Ephemeris astronomical calculation library compiled to WebAssembly for cross-platform JavaScript/TypeScript usage.

Features

• Cross-platform: Works in Deno, Node.js, browsers, and edge runtimes (Cloudflare Workers)
• High precision: Bit-level accuracy matching native Swiss Ephemeris calculations
• Complete API: 95+ functions for planetary positions, houses, eclipses, and more
• Zero dependencies: Self-contained WASM module with built-in Moshier ephemeris
• TypeScript: Full type definitions with TSDoc documentation

Installation

Deno / JSR

import { load } from "jsr:@fusionstrings/swisseph-wasi";

Node.js / npm

npm install @fusionstrings/swisseph-wasi

import { load } from "@fusionstrings/swisseph-wasi";

Browser

<script type="module">
  import { load } from "https://esm.sh/@fusionstrings/swisseph-wasi";
</script>

Quick Start

import { Constants, load } from "@fusionstrings/swisseph-wasi";

// Initialize the Swiss Ephemeris
const eph = await load();

// Calculate Julian Day for a date
const jd = eph.swe_julday(2024, 6, 15, 12.0, Constants.SE_GREG_CAL);

// Get Sun's position
const { xx, error } = eph.swe_calc_ut(
  jd,
  Constants.SE_SUN,
  Constants.SEFLG_SPEED,
);
console.log(`Sun longitude: ${xx[0]}°`);

// Calculate house cusps (Placidus, Zurich)
const { cusps, ascmc } = eph.swe_houses(jd, 47.3769, 8.5417, "P".charCodeAt(0));
console.log(`Ascendant: ${ascmc[0]}°`);
console.log(`MC: ${ascmc[1]}°`);

API Overview

Core Calculations

| Function | Description | | ------------------------------ | --------------------------- | | swe_calc / swe_calc_ut | Planetary positions (TT/UT) | | swe_houses / swe_houses_ex | House cusps and angles | | swe_julday / swe_revjul | Julian Day conversions | | swe_sidtime | Sidereal time | | swe_deltat | Delta T (TT - UT) |

Coordinate Systems

| Function | Description | | ------------------ | ---------------------------- | | swe_cotrans | Ecliptic ↔ Equatorial | | swe_azalt | Horizontal coordinates | | swe_set_sid_mode | Sidereal mode (Lahiri, etc.) | | swe_get_ayanamsa | Ayanamsa value |

Eclipses & Events

| Function | Description | | --------------------------- | ---------------------- | | swe_sol_eclipse_when_glob | Solar eclipse timing | | swe_lun_eclipse_when | Lunar eclipse timing | | swe_rise_trans | Rise/set/transit times |

Constants

Access astronomical constants via the Constants export:

import { Constants } from "@fusionstrings/swisseph-wasi";

Constants.SE_SUN; // 0 - Sun
Constants.SE_MOON; // 1 - Moon
Constants.SE_MERCURY; // 2 - Mercury
// ... etc.

Constants.SEFLG_SPEED; // Include velocities
Constants.SEFLG_SWIEPH; // Use Swiss Ephemeris files
Constants.SE_GREG_CAL; // Gregorian calendar

Using Ephemeris Files

By default, the library uses the built-in Moshier ephemeris. For higher precision, load Swiss Ephemeris data files:

const eph = await load({ ephePath: "./ephe" });

// Or mount files manually
const sepl_18 = await Deno.readFile("./ephe/sepl_18.se1");
eph.mount("sepl_18.se1", sepl_18);
eph.set_ephe_path(".");

Platform Support

| Platform | Status | Notes | | ------------------ | ------ | -------------------------- | | Deno | ✅ | Native support | | Node.js | ✅ | Via npm package | | Browser | ✅ | ESM bundle | | Cloudflare Workers | ✅ | Edge runtime compatible | | Bun | ✅ | Works with Node.js package |

License

AGPL-3.0 - Same license as the Swiss Ephemeris library.

This software is based on the Swiss Ephemeris by Astrodienst AG. See https://www.astro.com/swisseph/ for more information.

Credits

• Swiss Ephemeris by Astrodienst AG
• WASM compilation using WASI SDK