Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. XEphem is a Motif based ephemeris and planetarium program for Unix-like operating systems developed by Elwood C. Downey. 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. 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. The most recent version is 3.7.4 (July 2009). XEphem''s source code is available, but its free usage is restricted for personal and educational purposes only.