swisseph-wasm

SwissEph Quick Reference Guide

Basic Setup

import SwissEph from './src/swisseph.js';

const swe = new SwissEph();
await swe.initSwissEph();

// Your calculations here

swe.close(); // Always clean up

Essential Functions

Date & Time

// Julian Day calculation
const jd = swe.julday(2023, 6, 15, 12.5);

// UTC to Julian Day
const result = swe.utc_to_jd(2023, 6, 15, 12, 30, 0, swe.SE_GREG_CAL);

// Julian Day to calendar date
const date = swe.revjul(jd, swe.SE_GREG_CAL);

// Sidereal time
const sidTime = swe.sidtime(jd);

// Delta T
const deltaT = swe.deltat(jd);

Planet Positions

// Basic calculation
const pos = swe.calc_ut(jd, swe.SE_SUN, swe.SEFLG_SWIEPH);
// Returns: [longitude, latitude, distance, speed]

// Detailed calculation
const detailed = swe.calc(jd, swe.SE_MOON, swe.SEFLG_SWIEPH);
// Returns: {longitude, latitude, distance, longitudeSpeed, latitudeSpeed, distanceSpeed}

Sidereal Calculations

// Set sidereal mode
swe.set_sid_mode(swe.SE_SIDM_LAHIRI, 0, 0);

// Calculate sidereal position
const sidereal = swe.calc_ut(jd, swe.SE_SUN, swe.SEFLG_SWIEPH | swe.SEFLG_SIDEREAL);

// Get ayanamsa
const ayanamsa = swe.get_ayanamsa(jd);

Planet Constants

// Major planets
swe.SE_SUN = 0        swe.SE_JUPITER = 5
swe.SE_MOON = 1       swe.SE_SATURN = 6
swe.SE_MERCURY = 2    swe.SE_URANUS = 7
swe.SE_VENUS = 3      swe.SE_NEPTUNE = 8
swe.SE_MARS = 4       swe.SE_PLUTO = 9

// Lunar nodes
swe.SE_MEAN_NODE = 10
swe.SE_TRUE_NODE = 11

// Asteroids
swe.SE_CHIRON = 15    swe.SE_CERES = 17
swe.SE_PHOLUS = 16    swe.SE_PALLAS = 18

Calculation Flags

// Ephemeris types
swe.SEFLG_SWIEPH = 2      // Swiss Ephemeris (default)
swe.SEFLG_JPLEPH = 1      // JPL Ephemeris
swe.SEFLG_MOSEPH = 4      // Moshier Ephemeris

// Coordinate systems
swe.SEFLG_HELCTR = 8      // Heliocentric
swe.SEFLG_BARYCTR = 16384 // Barycentric
swe.SEFLG_TOPOCTR = 32768 // Topocentric
swe.SEFLG_EQUATORIAL = 2048 // Equatorial coordinates

// Special flags
swe.SEFLG_SPEED = 256     // Include speed
swe.SEFLG_SIDEREAL = 65536 // Sidereal positions
swe.SEFLG_RADIANS = 8192  // Results in radians
swe.SEFLG_J2000 = 32      // J2000 coordinates

Sidereal Modes

swe.SE_SIDM_FAGAN_BRADLEY = 0
swe.SE_SIDM_LAHIRI = 1
swe.SE_SIDM_DELUCE = 2
swe.SE_SIDM_RAMAN = 3
swe.SE_SIDM_KRISHNAMURTI = 5
swe.SE_SIDM_USER = 255

Common Patterns

Birth Chart Calculation

async function birthChart(year, month, day, hour, minute, timezone) {
  const swe = new SwissEph();
  await swe.initSwissEph();
  
  const utcHour = hour + minute / 60 - timezone;
  const jd = swe.julday(year, month, day, utcHour);
  
  const planets = [swe.SE_SUN, swe.SE_MOON, swe.SE_MERCURY, swe.SE_VENUS, 
                   swe.SE_MARS, swe.SE_JUPITER, swe.SE_SATURN];
  
  const chart = {};
  for (const planet of planets) {
    const pos = swe.calc_ut(jd, planet, swe.SEFLG_SWIEPH);
    chart[swe.get_planet_name(planet)] = pos[0];
  }
  
  swe.close();
  return chart;
}

Current Planetary Positions

async function currentPositions() {
  const swe = new SwissEph();
  await swe.initSwissEph();
  
  const now = new Date();
  const jd = swe.julday(
    now.getUTCFullYear(),
    now.getUTCMonth() + 1,
    now.getUTCDate(),
    now.getUTCHours() + now.getUTCMinutes() / 60
  );
  
  const sunPos = swe.calc_ut(jd, swe.SE_SUN, swe.SEFLG_SWIEPH);
  const moonPos = swe.calc_ut(jd, swe.SE_MOON, swe.SEFLG_SWIEPH);
  
  swe.close();
  
  return {
    sun: sunPos[0],
    moon: moonPos[0],
    julianDay: jd
  };
}

Sidereal vs Tropical

async function comparePositions(year, month, day, hour) {
  const swe = new SwissEph();
  await swe.initSwissEph();
  
  const jd = swe.julday(year, month, day, hour);
  
  // Tropical
  const tropical = swe.calc_ut(jd, swe.SE_SUN, swe.SEFLG_SWIEPH);
  
  // Sidereal (Lahiri)
  swe.set_sid_mode(swe.SE_SIDM_LAHIRI, 0, 0);
  const sidereal = swe.calc_ut(jd, swe.SE_SUN, swe.SEFLG_SWIEPH | swe.SEFLG_SIDEREAL);
  
  swe.close();
  
  return {
    tropical: tropical[0],
    sidereal: sidereal[0],
    difference: tropical[0] - sidereal[0]
  };
}

Utility Functions

// Normalize degrees (0-360)
const normalized = swe.degnorm(370); // Returns 10

// Split degrees into D°M'S"
const split = swe.split_deg(123.456, swe.SE_SPLIT_DEG_ROUND_SEC);
// Returns: {degree: 123, min: 27, second: 24, sign: 4}

// Day of week (0=Monday, 6=Sunday)
const dayOfWeek = swe.day_of_week(jd);

// Planet name
const name = swe.get_planet_name(swe.SE_SUN); // Returns "Sun"

// Version info
const version = swe.version();

Error Handling Template

async function safeCalculation() {
  let swe = null;
  
  try {
    swe = new SwissEph();
    await swe.initSwissEph();
    
    // Your calculations here
    const jd = swe.julday(2023, 6, 15, 12);
    const result = swe.calc_ut(jd, swe.SE_SUN, swe.SEFLG_SWIEPH);
    
    return { success: true, data: result };
    
  } catch (error) {
    return { success: false, error: error.message };
  } finally {
    if (swe) swe.close();
  }
}

Performance Tips

  1. Reuse instances for multiple calculations
  2. Batch calculations in single session
  3. Always call close() to prevent memory leaks
  4. Validate inputs before calculation
  5. Use appropriate flags for your needs

Common Gotchas

Browser Requirements

File Structure

your-project/
├── src/
│   └── swisseph.js          # Main library
├── wasm/
│   ├── swisseph.js          # WASM module
│   └── swisseph.wasm        # WASM binary
└── your-app.js              # Your application
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