The SWISS EPHEMERIS is the high precision ephemeris developed by Astrodienst, largely based upon the DExxx ephemerides from NASA's JPL . The original release in 1997 was based on the DE405/406 ephemeris. Since release 2.00 in February 2014, it is based on the DE431 ephemeris released by JPL in September 2013.

Developers can license the Ephemeris library. Ephemeris users find more than 8000 years of read-made printable files of ephemerides, containing tens of thousands print pages in PDF quality.

The Swiss Ephemeris offers these advantages:

  • The Swiss Ephemeris is based upon the planetary and lunar ephemeris DE431 developed by NASA's Jet Propulsion Laboratory. It covers the time range 13201 BC to AD 17191. These data have been further compressed with sophisticated compression techniques developed by Astrodienst. This compressed ephemeris reproduces the JPL data with 0.001 arcseconds precision. The Swiss Ephemeris files for the planets without the Moon take up 27 Mb disk space, the files for the Moon take up 70 Mb, totally 97 Mb disk space. The original JPL file takes up 2788 Mb disk space.

  • All transformation steps from the inertial timeframe of the JPL DE430/431 integration to the reference frame for astrological coordinates (true equinox of date), all corrections like relativistic aberration, deflection of light in the gravity field of the Sun etc. have been performed with utmost care and precision so that the target precision of 0.001 arcsec is maintained through all transformation steps. Never before has such a high precision ephemeris been available to astrologers. 

  • Swiss Ephemeris contains three ephemerides. The user can choose whether he/she wants to use the original JPL DE431 data (if available at their site), the compressed Swiss Ephemeris data (the default) or a built in semianalytic theory by Steve Moshier. The Swiss Ephemeris package switches automatically to the available best precision ephemeris dependent on which installed ephemeris files it finds. Even without any stored ephemeris files, using the Moshier model, planetary positions with better than 0.1 seconds of arc precision are available (3 arcsec for the Moon). The Moshier ephemeris is based on DE404 and covers the time range 3000 BC – 3000 AD.

  • In addition to the astronomical planets as contained in the JPL integration, we have included all other bodies and hypothetical factors which are of interest to the astrologer. We have used our own numerical integration program to provide ephemerides for all known asteroids, once they are officially numbered. There are, at the time of this writing in February 2014, over 385'000 of them and nobody will be able to use them all. We distribute these extended asteroid files via the download area.

  • Speed: The Swiss Ephemeris is precise and fast. On our Linux test machine, we compute 10'000 complete sets of planetary positions, i.e. 10'000 x 11 planets, in less than 3 seconds. This is 0.3 milliseconds for the complete set of exact planetary positions (consecutive 1 day steps).

How to license the Swiss Ephemeris:

The Swiss Ephemeris is not a product for end users. It is a toolset for programmers to build into their astrological software.

Swiss Ephemeris is made available by its authors under a dual licensing system. The software developer, who uses any part of Swiss Ephemeris in his or her software, must choose between one of the two license models, which are

  • a) GNU Affero General Public License (AGPL)

  • b) Swiss Ephemeris Professional License

The choice must be made before the software developer distributes software containing parts of Swiss Ephemeris to others, and before any public service using the developed software is activated.

If the developer choses the AGPL software license, he or she must fulfill the conditions of that license, which includes the obligation to place his or her whole software project under the AGPL or a compatible license.

If the developer choses the Swiss Ephemeris Professional license, he must follow the instructions below and purchase the Swiss Ephemeris Professional Edition from Astrodienst and sign the corresponding license contract.

The License grants you the right to use, copy, modify and redistribute Swiss Ephemeris, but only under certain conditions described in the License. Among other things, the License requires that the copyright notices and this notice be preserved on all copies.

Authors of the Swiss Ephemeris: Dieter Koch and Alois Treindl

The authors of Swiss Ephemeris have no control or influence over any of the derived works, i.e. over software or services created by other programmers which use Swiss Ephemeris functions.

The names of the authors or of the copyright holder (Astrodienst) must not be used for promoting any software, product or service which uses or contains the Swiss Ephemeris. This copyright notice is the ONLY place where the names of the authors can legally appear, except in cases where they have given special permission in writing.

Both types of licenses include the right to use the label 'Swiss Ephemeris Inside' on products.

If you want the Swiss Ephemeris Professional License for your software project, please proceed as follows:

  • print the licensing contract in two copies

  • fill the printed copies out and sign them

  • mail them to Astrodienst AG, Dammstr. 23, 8702 Zollikon, Switzerland, or send a signed and scanned complete PDF to .

  • do not forget the credit card details (if you live outside D,CH,A where we deliver with invoice). Bank transfer is also an option.

  • we will countersign the contract and send it to you. We will charge your credit card when we send the signed contract.

If you want the Swiss Ephemeris Free Edition for your software project, please proceed as follows:

The documentation

The Swiss Ephemeris documentation consists of two parts. 

The General Manual describes our work and the technical background. 

The Programmer's Manual describes the implementation details and the programming interface to the DLL resp. library functions. 

Demo Programs can be downloaded from . A utility unzip.exe is also provided to unpack the download archive format.

  • swewin.exe is a Windows program which computes complete horoscopes including houses and asteroids.

  • swetest.exe is a command line Windows program which computes planetary positions. It is very versatile and can be used to create tables of ephemerides, or other tabular data for export to Excel and similar tools.
    Issue the command
    swetest -?
    to get information about the features of swetest.

Authors: Dieter Koch and Dr. Alois Treindl