# ๐ astrosk-wasm
### *Swiss Ephemeris, reborn in WebAssembly*
**Lightweight ยท TypeScript-first ยท Browser + Node + Angular**
[](https://www.npmjs.com/package/astrosk-wasm)
[](./LICENSE)
[](https://www.astro.com/swisseph/)
[](https://nodejs.org/)
[](https://www.typescriptlang.org/)
[](#-verified-against-jagannatha-hora)
[](#-verified-against-jagannatha-hora)
๐ **[astrosk.com](https://astrosk.com)** ยท ๐ฆ **[npm](https://www.npmjs.com/package/astrosk-wasm)** ยท ๐ **[GitHub](https://github.com/skota-in/astrosk-wasm)**
---
## โจ What is this?
**`astrosk-wasm`** ports the official **Swiss Ephemeris C library** (`2.10.03` โ the final upstream release) to **WebAssembly**, so you get the *exact same* astronomical math the reference C implementation produces โ now usable from the browser, Node, or any modern JS runtime.
```mermaid
flowchart LR
A[Swiss Ephemeris C
v2.10.03 final] -->|Emscripten| B[astrosk.wasm]
B --> C[TypeScript wrapper
Astrosk class]
C --> D[๐ Browser]
C --> E[๐ข Node.js]
C --> F[๐
ฐ๏ธ Angular]
C --> G[๐ฆ Any JS runtime]
style A fill:#1e293b,stroke:#8b5cf6,stroke-width:2px,color:#fff
style B fill:#7c3aed,stroke:#a78bfa,stroke-width:2px,color:#fff
style C fill:#0891b2,stroke:#22d3ee,stroke-width:2px,color:#fff
style D fill:#16a34a,stroke:#4ade80,color:#fff
style E fill:#16a34a,stroke:#4ade80,color:#fff
style F fill:#16a34a,stroke:#4ade80,color:#fff
style G fill:#16a34a,stroke:#4ade80,color:#fff
```
---
## ๐ฏ Features at a glance
| | |
|---|---|
| ๐ช **Planetary positions** | Sun, Moon, planets, nodes, asteroids โ tropical or sidereal |
| ๐ **House systems** | Placidus, Koch, Equal, Whole Sign, and 20+ more |
| ๐๏ธ **Vedic / sidereal** | True Chitra, True Pushya, Lahiri, Krishnamurti, and dozens more |
| โก **Pre-allocated scratch** | Reusable heap buffers โ fast in the hot path |
| ๐งญ **Smart `setEphePath`** | Auto-detects URL ยท Node dir ยท virtual FS โ one method, all environments |
| ๐ฆ **Tree-shakeable** | Tiny TS wrapper; WASM is fetched on demand |
| ๐งช **Verified** | 80/80 JHora reference checks + `swetest` C-binary parity on every build |
---
## โ
Verified against Jagannatha Hora
> ๐ชท **Vedic astrologers can trust the numbers.**
Every release is validated against **8 reference charts produced by Jagannatha Hora 8.0** (PVR Narasimha Rao):
| Ayanamsa |
Charts |
Coverage |
Tolerance |
| ๐ True Chitra |
4 |
๐ฎ๐ณ India ยท ๐บ๐ธ USA ยท ๐ฏ๐ต Japan ยท ๐ฌ๐ง UK
2010โ2025 |
Sub-arcsecond โจ
(80/80 checks pass) |
| ๐ True Pushya |
4 |
The reference printouts live in [`examples/chart{1..8}.txt`](./examples) and the test runs locally:
```bash
๐ npm run build
๐งช npm run test:jhora
```
### ๐ How to call the API to match JHora
JHora displays the **mean / geometric** sidereal position โ *no nutation, no light-time aberration*. To reproduce its output, combine `SWIEPH | NONUT | TRUEPOS` on every ayanamsa and `calcUt` call:
```ts
import { Astrosk, SE } from 'astrosk-wasm';
const astrosk = await Astrosk.init();
// 1๏ธโฃ Pick the ayanamsa JHora is configured for.
astrosk.setSidMode(SE.SIDM.TRUE_PUSHYA); // or TRUE_CITRA, LAHIRI, etc.
// 2๏ธโฃ Convert local civil time โ UT, then to a Julian Day.
// JHora prints "Time Zone: 5:30:00 (East of GMT)" โ UT = local - 5.5h.
const jdUt = astrosk.julday(2025, 5, 10, 5.2395); // 10:44:22 IST = 05:14:22 UT
// 3๏ธโฃ Read the ayanamsa with the JHora-matching flags.
const JHORA = SE.FLG.SWIEPH | SE.FLG.NONUT | SE.FLG.TRUEPOS;
const ayanamsa = astrosk.getAyanamsaExUt(jdUt, JHORA);
// 4๏ธโฃ Compute sidereal planet longitudes with the same flags + SIDEREAL.
const sun = astrosk.calcUt(jdUt, SE.SUN, JHORA | SE.FLG.SIDEREAL | SE.FLG.SPEED);
console.log(sun.longitude); // matches JHora's "Sun ... longitude" line
// 5๏ธโฃ Ketu is geometric: Rahu + 180ยฐ.
const rahu = astrosk.calcUt(jdUt, SE.MEAN_NODE, JHORA | SE.FLG.SIDEREAL | SE.FLG.SPEED);
const ketu = (rahu.longitude + 180) % 360;
```
> โ ๏ธ If you instead use plain `SE.FLG.SWIEPH`, you get the **apparent** position (with nutation + aberration applied) โ astronomically correct but **20โ40 arcsec off JHora's display**. Pick the convention that matches your upstream reference and use it consistently.
---
## ๐ Install
```bash
npm install astrosk-wasm
# or
pnpm add astrosk-wasm
# or
yarn add astrosk-wasm
```
---
## โก Quick start
```ts
import { Astrosk, SE } from 'astrosk-wasm';
const astrosk = await Astrosk.init();
// ๐ Point Swiss Ephemeris at your ephemeris files.
// Auto-detects URL base (browser) vs. local directory (Node).
await astrosk.setEphePath('/assets/ephe'); // ๐ browser
// await astrosk.setEphePath('C:/ephe'); // ๐ข Node, custom dir
// ๐๏ธ May 10, 2026 11:32:26 UT
const jd = astrosk.julday(2026, 5, 10, 11.540556);
// โ๏ธ Tropical
const sun = astrosk.calcUt(jd, SE.SUN, SE.FLG.SWIEPH | SE.FLG.SPEED);
console.log('Sun longitude:', sun.longitude); // 49.8273ยฐ
// ๐๏ธ Sidereal (Vedic) โ True Pushya ayanamsa (PVR Narasimha Rao)
astrosk.setSidMode(SE.SIDM.TRUE_PUSHYA);
const sunSid = astrosk.calcUt(
jd, SE.SUN, SE.FLG.SWIEPH | SE.FLG.SIDEREAL | SE.FLG.SPEED,
);
console.log('Sun sidereal:', sunSid.longitude); // 26.7361ยฐ
// ๐ Houses (Placidus)
const houses = astrosk.houses(jd, 42.20278, -71.68611, 'P');
console.log('Ascendant:', houses.ascmc[0]);
console.log('MC:', houses.ascmc[1]);
astrosk.close();
```
---
## ๐ How `setEphePath` works
One method, three sources โ auto-detected.
```mermaid
flowchart TD
A([๐ setEphePath source, options?]) --> B{What kind
of source?}
B -->|http:// or https://| C[๐ URL base]
B -->|/ephe path inside WASM FS| D[๐พ Virtual FS path]
B -->|Path exists on Node disk| E[๐ข Node directory]
B -->|Anything else| C
C --> C1[fetch /name for each file]
C1 --> F[mod.FS.writeFile /ephe/name, bytes]
E --> E1[fs.readFile join dir, name]
E1 --> F
D --> G([โ
swe_set_ephe_path /ephe])
F --> G
style A fill:#7c3aed,stroke:#a78bfa,color:#fff,stroke-width:2px
style B fill:#1e293b,stroke:#fbbf24,color:#fff,stroke-width:2px
style C fill:#0891b2,stroke:#22d3ee,color:#fff
style D fill:#0891b2,stroke:#22d3ee,color:#fff
style E fill:#0891b2,stroke:#22d3ee,color:#fff
style F fill:#16a34a,stroke:#4ade80,color:#fff
style G fill:#ec4899,stroke:#f9a8d4,color:#fff,stroke-width:2px
```
Default file list (overridable via `{ files: [...] }`):
| File | Purpose | Size |
|------|---------|------|
| ๐ช `sepl_18.se1` | Planets, 1800โ2400 AD | ~476 KB |
| ๐ `semo_18.se1` | Moon, 1800โ2400 AD | ~1.3 MB |
| โฑ๏ธ `seleapsec.txt` | Leap seconds | tiny |
| โญ `sefstars.txt` | Fixed stars catalog | small |
| ๐ `seorbel.txt` | Orbital elements | small |
---
## ๐
ฐ๏ธ Angular integration
```ts
// src/app/astrosk.service.ts
import { Injectable } from '@angular/core';
import { Astrosk, SE } from 'astrosk-wasm';
@Injectable({ providedIn: 'root' })
export class AstroskService {
private instance?: Astrosk;
private initPromise?: Promise;
async getInstance(): Promise {
if (this.instance) return this.instance;
if (this.initPromise) return this.initPromise;
this.initPromise = (async () => {
const astrosk = await Astrosk.init();
// ๐ฏ Auto-detects URL base; fetches the default file set in parallel.
await astrosk.setEphePath('/assets/ephe');
this.instance = astrosk;
return astrosk;
})();
return this.initPromise;
}
async sunLongitude(date: Date): Promise {
const a = await this.getInstance();
const hours = date.getUTCHours()
+ date.getUTCMinutes() / 60
+ date.getUTCSeconds() / 3600;
const jd = a.julday(
date.getUTCFullYear(),
date.getUTCMonth() + 1,
date.getUTCDate(),
hours,
);
return a.calcUt(jd, SE.SUN).longitude;
}
}
```
๐ Configure assets in `angular.json`:
```json
"assets": [
{
"glob": "**/*",
"input": "node_modules/astrosk-wasm/wasm",
"output": "/wasm"
},
{
"glob": "**/*",
"input": "node_modules/astrosk-wasm/deps/ephe",
"output": "/assets/ephe"
}
]
```
If your bundler does not auto-resolve `astrosk.wasm`, locate it explicitly:
```ts
const astrosk = await Astrosk.init({
locateWasm: '/wasm/astrosk.wasm',
});
```
---
## ๐ Ephemeris files
The npm package ships with a **minimal set** covering the 9 classical planets (Sun โ Pluto) for years **1800โ2400 AD**.
```mermaid
flowchart LR
A[๐ฏ Date range needed] --> B{Year}
B -->|1800โ2400 AD| C[โ
Bundled .se1]
B -->|Wider range| D[โฌ๏ธ Fetch from astro.com
or load via setEphePath/
loadEphemerisFile]
B -->|Anywhere| E[๐งฎ Moshier fallback
SE.FLG.MOSEPH]
C --> Z[๐ช calcUt jd, body, flags]
D --> Z
E --> Z
style A fill:#7c3aed,stroke:#a78bfa,color:#fff,stroke-width:2px
style B fill:#1e293b,stroke:#fbbf24,color:#fff
style C fill:#16a34a,stroke:#4ade80,color:#fff
style D fill:#0891b2,stroke:#22d3ee,color:#fff
style E fill:#f59e0b,stroke:#fbbf24,color:#fff
style Z fill:#ec4899,stroke:#f9a8d4,color:#fff,stroke-width:2px
```
- ๐ Wider date ranges: download from [astro.com/ftp/swisseph/ephe](https://www.astro.com/ftp/swisseph/ephe/) and pass the directory to `setEphePath` (Node) or host them and pass a URL base (browser).
- ๐ฐ๏ธ **JPL DE441** (~3 GB): serve `de441.eph` from your CDN, call `setJplFile('de441.eph')`, and use `SE.FLG.JPLEPH`. **Not bundled** because of its size.
- ๐งฎ **Moshier fallback**: no ephemeris file needed when you pass `SE.FLG.MOSEPH`. Accuracy โ 0.01โณ (Sun) โ 7โณ (Moon). Fine for general astrology; not professional astronomy.
---
## ๐ API reference
### `Astrosk.init(options?)`
Returns a `Promise`.
| Option | Type | Description |
|---|---|---|
| `ephePath?` | `string` | Virtual FS path for ephemeris. Default `/ephe`. |
| `locateWasm?` | `string \| ((defaultUrl) => string) \| ArrayBuffer` | Override WASM binary location. |
| `noEphePath?` | `boolean` | Skip auto-call to `swe_set_ephe_path`. |
### ๐๏ธ Date / time
| Method | Returns |
|---|---|
| `julday(year, month, day, hour, gregFlag?)` | `number` โ Julian Day |
| `revjul(jd, gregFlag?)` | `{ year, month, day, hour }` |
| `utcToJd({year, month, day, hour, minute, second})` | `{ jdEt, jdUt }` |
| `deltaT(jd)` | `number` โ seconds |
| `sidtime(jd)` | `number` โ hours |
### ๐ช Planets
| Method | Returns |
|---|---|
| `calcUt(jdUt, body, flags?)` | `CalcResult` |
| `calc(jdEt, body, flags?)` | `CalcResult` |
| `getPlanetName(planet)` | `string` |
### ๐๏ธ Ayanamsa / sidereal
| Method | Returns |
|---|---|
| `setSidMode(mode, t0?, ayan_t0?)` | `void` |
| `getAyanamsaUt(jdUt)` | `number` โ degrees |
| `getAyanamsaExUt(jdUt, flags?)` | `number` โ degrees โจ *preferred* |
| `getAyanamsaName(mode)` | `string` |
### ๐ Houses
| Method | Returns |
|---|---|
| `houses(jdUt, lat, lon, hsys?)` | `HousesResult` |
| `housesEx(jdUt, flags, lat, lon, hsys?)` | `HousesResult` |
### ๐ Ephemeris sources
- **`setEphePath(source, options?)`** โ `Promise` โ auto-detects:
- ๐ **URL base** (`/assets/ephe`, `https://...`) โ fetches each file in the default list and writes it into the WASM virtual FS.
- ๐ข **Node directory** (`C:/ephe`, `/usr/share/ephe`) โ reads from disk via `fs.readFile`.
- ๐พ **Virtual FS path** (`/ephe`) โ just points Swiss Ephemeris at an already-populated location (e.g. files staged via `loadEphemerisFile`).
- Options: `{ files?: readonly string[]; optional?: boolean }`. Defaults to `DEFAULT_EPHE_FILES`, silently skips missing files.
- **`loadEphemerisFile(name, bytes)`** โ low-level: write a single file into the virtual FS. Use when bytes come from a source `setEphePath` doesn't handle (IndexedDB, in-memory cache, etc.).
- **`setJplFile(name)`**
### โป๏ธ Lifecycle
| Method | Notes |
|---|---|
| `setTopo(lon, lat, alt?)` | Topocentric observer |
| `version()` | Library version string |
| `close()` | ๐งน Frees native scratch buffers โ **required** to avoid leaks |
---
## ๐งช Verification
```mermaid
flowchart TB
A[๐ astrosk-wasm release] --> B[๐งช tests/verify.mjs]
A --> C[๐งช tests/jhora.spec.ts]
B --> B1["Compare every value vs.
native swetest CLI
(Swiss Ephemeris 2.10.03 C)"]
B1 --> B2[Tolerance: 1e-6ยฐ โ 3.6 mas]
C --> C1[8 JHora reference printouts
4 True Chitra ยท 4 True Pushya]
C1 --> C2[80 / 80 ayanamsa + planet checks]
B2 --> Z([โ
Ship it])
C2 --> Z
style A fill:#7c3aed,stroke:#a78bfa,color:#fff,stroke-width:2px
style B fill:#0891b2,stroke:#22d3ee,color:#fff
style C fill:#0891b2,stroke:#22d3ee,color:#fff
style B1 fill:#1e293b,stroke:#475569,color:#e2e8f0
style B2 fill:#1e293b,stroke:#475569,color:#e2e8f0
style C1 fill:#1e293b,stroke:#475569,color:#e2e8f0
style C2 fill:#1e293b,stroke:#475569,color:#e2e8f0
style Z fill:#16a34a,stroke:#4ade80,color:#fff,stroke-width:2px
```
```bash
๐ npm run build
๐งช npm test # swetest suite (tropical + sidereal vs. C reference)
๐ชท npm run test:jhora # JHora suite (8 reference charts)
```
---
## ๐ License
`astrosk-wasm` is licensed under the **GNU Affero General Public License v3.0 or later** ([AGPL-3.0-or-later](./LICENSE)).
This project incorporates the [Swiss Ephemeris](https://github.com/aloistr/swisseph) by Astrodienst AG (ยฉ 1997โ2021), used under AGPL-3.0. See [NOTICE](./NOTICE) for full attribution.
### ๐ A note on the AGPL network clause
Because AGPL-3.0 ยง13 applies, any public network service that embeds `astrosk-wasm` must offer its users access to the complete corresponding source code of the deployed version. **AstroSK** satisfies this by making its source publicly available at with releases tagged to match deployments.
### ๐ผ Commercial use
If the AGPL is incompatible with your project, you cannot use `astrosk-wasm` directly โ you must obtain a [Swiss Ephemeris Professional License](https://www.astro.com/swisseph/) directly from Astrodienst AG and link against the upstream Swiss Ephemeris under that license.
---
## ๐ซ Credits
- ๐ช [**Swiss Ephemeris**](https://www.astro.com/swisseph/) by Astrodienst AG โ the foundation everything here is built on.
- ๐ชท **PVR Narasimha Rao** โ [Jagannatha Hora](http://www.vedicastrologer.org/) is the reference standard we validate against.
- ๐ [**astrosk.com**](https://astrosk.com) โ the home of the AstroSK ecosystem.
---
**Built with โค๏ธ for astronomers, astrologers, and the curious.**
[โฌ back to top](#-astrosk-wasm)