swiss-ephemeris

Haskell bindings for the Swiss Ephemeris library.

See the tests in the spec folder for thorough example usage, but here's a simple "main" that demonstrates the current abilities, inspired by the sample program in the official library:

import SwissEphemeris

main :: IO
main = do 
  -- location of your ephemeris directory. We bundle a sample one in `swedist`.
  withEphemerides "./swedist/sweph_18" $ do
    let time = julianDay 1989 1 6 0.0
        place = GeographicPosition {geoLat = 14.0839053, geoLng = -87.2750137}
  
    -- locate all bodies between the Sun and Chiron
    forM_ [Sun .. Chiron] $ \planet -> do
      -- if no ephemerides data is available for the given planetary body, a `Left` value
      -- will be returned.
      coord <- calculateEclipticPosition time planet
      putStrLn $ show planet <> ": " <> show coord
   
    -- Calculate cusps for the given time and place, preferring the `Placidus` system.
    -- note that the underlying library may decide to use the `Porphyrius` system if it can't
    -- calculate cusps (happens for the Placidus and Koch systems in locations near the poles.)
    cusps <- calculateCusps Placidus time place
    putStrLn $ "Cusps: " <> show cusps

The above should print the ecliptic latitude and longitude (plus some velocities) for all planets, and then the cusps and other major angles (ascendant, mc, ARMC, alternative angles.)

There's withEphemerides to run calculations using a particular ephemerides directory and then close any used system resources, and withoutEphemerides to use the default ephemerides ("Moshier.")

To see actual results and more advanced usage, check out the tests. For some more advanced examples, see swetest.c and swemini.c in the csrc directory: they're the test/example programs provided by the original authors. You can also play around with the C library via the authors' test page.

Notes

All the code in the csrc folder comes directly from the latest official tarball, v2.09.03.

The swedist folder includes the original documentation from the tarball in PDF (see the doc) folder, and a copy of ephemeris data files.

For other formats of the original documentation, see: https://www.astro.com/ftp/swisseph/doc/

The authors also host HTML versions of the manuals. Two are provided, a general reference and a programming reference. Both are very useful to get acquainted with the functionality and implementation details.

• General Reference
• Programmer's Reference

Ephemerides files

As noted in the original documentation you can omit the setEphemerides call (or use setNoEphemerides, or the withoutEphemerides bracket function) and calculations will use a built-in analytical ephemeris ("Moshier") which:

provides "only" a precision of 0.1 arc seconds for the planets and 3" for the Moon. No asteroids will be available, and no barycentric option can be used.

Note that if you're interested in the asteroid Chiron (which is common in astrological practice these days,) you'll have to procure Ephemerides files and shouldn't use the default ephemerides.

For convenience, we bundle a few ephemerides files in this repository (see swedist) for the time range 1800 AD – 2399 AD. If you were born before that, or plan to code e.g. transits for after that (!) or you'd prefer even more precision, you can download more ephemerides files from the astro.com downloads page

I chose the bundled files due to this comment in the official docs:

If the [JPL] file is too big, then you can download the files sepl_18.se1 and semo_18.se1 from here: http://www.astro.com/ftp/swisseph/ephe/

For a full explanation of the files available, see the Description of the Ephemerides section of the original manual, also of interest is the comparison between the Swiss Ephemeris and the raw NASA JPL data.

Contributing

I've only made available the types and functions that are useful for my own, traditional, horoscope calculations. Feel free to add more! See the astro.com documentation for ideas.