@fusionstrings/swiss-eph

Swiss Ephemeris astronomical calculation library compiled to WebAssembly for cross-platform JavaScript/TypeScript usage, with idiomatic Rust bindings.

Features

• Cross-platform: Works in Deno, Node.js, browsers, and edge runtimes (Cloudflare Workers)
• 3x2x4 Support: 3 entrypoint styles across 2 build types on all 4 platform families
• Rust Bindings: Complete FFI and safe Rust API for native performance
• 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 or WASI package
• TypeScript: Full type definitions with TSDoc documentation

Platform Support Matrix (3x2x4 = 24 Combinations)

We support 24 distinct integration paths. See EXAMPLES.md for exhaustive code and caveats.

#	Platform	Builds	Entrypoint Styles	Status
1-6	Deno	wasmbuild, wasi	JS API, Direct WASM, Inline	✅
7-12	Node.js	wasmbuild, wasi	JS API, Direct WASM, Inline	✅
13-18	Browser	wasmbuild, wasi	JS API, Direct WASM, Inline	✅
19-24	Worker	wasmbuild, wasi	JS API, Direct WASM, Inline	✅

Tip

The 3x2x4 matrix covers 3 Styles (JS API, Direct WASM, Inline) x 2 Builds (wasmbuild, wasi) x 4 Platforms (Deno, Node, Browser, Worker).

Installation

Deno / JSR

import { Constants, SwissEph } from "jsr:@fusionstrings/swiss-eph/wasi";

Node.js (via JSR)

npx jsr add @fusionstrings/swiss-eph

import { Constants, SwissEph } from "@fusionstrings/swiss-eph/wasi";

Quick Start (JS/TS)

import { Constants, load } from "@fusionstrings/swiss-eph";

// 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]}°`);

Rust Usage

Add this to your Cargo.toml:

[dependencies]
swiss-eph = "0.1.0"

Quick Start (Rust)

use swisseph_x::safe::*;
use swisseph_x::*;

fn main() {
    let jd = julday(2024, 1, 1, 12.0);
    let flags = CalcFlags::new().with_speed();
    let sun = calc(jd, SE_SUN, flags).unwrap();
    println!("Sun longitude: {:.6}°", sun.longitude);
}

Ephemeris Data

Swiss Ephemeris supports three modes of operation:

1. Moshier Mode (Default, No Files Needed)

Works out of the box with ~1 arcsecond precision:

// Just use the library - falls back to Moshier automatically
let sun = safe::calc_ut(jd, SE_SUN, flags)?;

2. Embedded Data (Optional Feature)

Add ~1.7 MB of embedded ephemeris for higher precision (1800-2400 CE):

[dependencies]
swiss-eph = { version = "0.1", features = ["embedded-ephe"] }

3. Manual Download (Full Control)

Download ephemeris files from astro.com:

curl -O https://www.astro.com/ftp/swisseph/ephe/sepl_18.se1
curl -O https://www.astro.com/ftp/swisseph/ephe/semo_18.se1

Then configure:

safe::set_ephe_path("/path/to/ephe/files");

API Overview (JS/TS)

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)

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 and wasmbuild