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XEphem Screenshot.png
Screenshot of the XEphem 3.7.2 with the Earth and sky views
Developer(s)Elwood C. Downey
Initial release1990; 32 years ago (1990) [1]
Stable release
4.0.2[2] / February 28, 2021; 16 months ago (2021-02-28)
Written inC and Motif
Operating systemUnix-like
TypePlanetarium software
LicenseMIT License

XEphem is a Motif based ephemeris and planetarium program for Unix-like operating systems developed by Elwood C. Downey.


XEphem started as a Unix and Motif conversion of the IBM PC-based ephem. It was initially released in December 1993 with version 2.5.[citation needed] Its commercial edition was discontinued in 2016; the free version continued to be offered as proprietary software.[3] In 2021, however, Downey relicensed XEphem's source code under the MIT License, raising the release version from 3.7.7 to 4.0.0 to highlight the change.[4]

Algorithms and models[edit]

XEphem uses

and includes

and other specialized catalogs. It also include the Digital Lunar Orbiter Photographic Atlas of the Moon.[7] XEphem is a client for Internet data sources such as the Digitized Sky Survey, Solar and Heliospheric Observatory, AAVSO light curves, and global temperature and cloud coverage. Through the Instrument Neutral Distributed Interface, XEphem can control some models of amateur telescopes, such as by Meade, Celestron, and Vixen, and auxiliary telescope components.


While the free version of XEphem only includes a subset of the SKYMAP Master Catalog and the Messier Catalog, the internal format of the remaining catalogs can be inferred from the source code, and e.g. the internal binary Tycho-2 catalog can be generated from the original data.[8] This is also possible for the non-stellar catalogs in the ASCII .edb format, such as for HYPERLEDA.[9]

XEphem can also read several astrometric catalogs in their original formats:

Numerical routines are used in PyEphem with permission of Elwood Downey.[14]

See also[edit]


  1. ^ "XEphem history". Retrieved 2015-09-28.
  2. ^ Downey, Elwood (2021-02-28). "Xephem installation on Ubuntu 20.02". Groups.io. Archived from the original on 2021-05-29. Retrieved 2021-05-29.
  3. ^ Downey, Elwood (2016-10-31). "thanks for using XEphem". Groups.io. Archived from the original on 2021-05-29. Retrieved 2021-05-29.
  4. ^ Downey, Elwood (2021-02-07). "XEphem now released under MIT Open Source license". Groups.io. Archived from the original on 2021-05-29. Retrieved 2021-05-29.
  5. ^ Chapront, J. (1995). "Representation of planetary ephemerides by frequency analysis. Application to the five outer planets". Astronomy and Astrophysics Supplement Series. 109: 181. Bibcode:1995A&AS..109..181C.
  6. ^ J. Meeus, Astronomical Formulae for Calculators (Willmann-Bell, Richmond, VA, 1982).
  7. ^ Digital Lunar Orbiter Photographic Atlas of the Moon
  8. ^ see e.g. Programs to generate XEphem 3.4 xe2 catalogs
  10. ^ CDS VizieR Guide Star Catalog
  11. ^ CDS VizieR GSC-ACT
  12. ^ USNO PMM catalogs
  13. ^ CDS VizieR UCAC2
  14. ^ "PyEphem Home Page".

External links[edit]