Free Ephemeris Software

Vincent Van Gogh, The Starry Night    
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ephemeris - Latin, originally from the Greek "ephémeros, -on," daily. An almanac of the daily motions of the planets and stars.
ephemeris.com - A website devoted to information about time and motion in the universe.

The ephemeris.com Software Library

ephemeris.com is pleased to offer Version 1.0 of the ephemeris.com software library. This software reads and writes NASA's Jet Propulsion Laboratory planetary ephemeris files, and calculates positions and velocities with the full precision of the original JPL software, which is written in FORTRAN. This library is written in C, and is made available for free under the Lesser Gnu Public License. The LGPL allows you to use the software for free (but without any warranty), even if you use it in software you intend to sell.

For a general overview, see the README.txt file (corrected on 28 May 2004, with correction added to distribution below). For the full terms of the Lesser Gnu Public License version 2.1, see LICENSE.txt.

If you use this software, reference to "The ephemeris.com Software Library" or http://www.ephemeris.com/software.html would be greatly appreciated. That will help anyone interested in finding the latest copy. Please also credit Dr. E. Myles Standish of NASA's Jet Propulsion Laboratory for the JPL ephemeris files (DE200, DE405, DE406, etc.).

The software is available as a gzipped tarball or a Winzip archive:

E-mail any questions to mystars@ephemeris.com. Send bug reports to bugs@ephemeris.com.

Known Bugs and Future Update

There is one known bug: velocities calculated in AU/second or kilometers/second are not computed correctly because of a misplaced multiplication in ephcom_get_coords(). This will be fixed in the next update. AU/day and kilometers/day report correct results. All of the example programs use AU/day.

The next update will be available "real soon" (as of September 2004). If you would like notification when it is available, please send an email to mystars@ephemeris.com and put "update" somewhere in the subject of your email.

There will be one big change in the next version: the #define values for EPHCOM_MERCURY and up will start at zero, not at one. Astrometric positions will also be available, along with other routines for local observation.

NASA/JPL Planetary Data

The U.S. Naval Observatory uses the current JPL ephemeris, DE405, to compute positions in The Astronomical Almanac. You can obtain a free copy of DE405 at JPL's FTP site, ftp://ssd.jpl.nasa.gov/pub/eph/export/. If you do download the data from JPL, you can test the software library using DE405 by following these steps:

JPL also produces the JPL Planetary and Lunar Ephemerides on CD-ROM, by Dr. Myles Standish et al., available through Willmann-Bell Publishers for approximately $25. JPL's CD contains

The ephemeris.com software library was tested with DE200, DE405, and DE406 using the JPL CD. Typing 'make test' will test operation with all three of these ephemerides across their entire range.

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Copyright 2004. All Rights Reserved.