Xephem is an interactive astronomical ephemeris program for the X Window
system. It ...
computes heliocentric, geocentric and topocentric information for fixed
celestial objects and objects in heliocentric and geocentric orbits;
has built-in support for all planet positions; the moons of Jupiter, Saturn
and Earth; Mars' and Jupiter's central meridian longitude; Saturn's rings;
and Jupiter's Great Red Spot
WWW: http://www.clearskyinstitute.com/xephem/
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