aa56 is a C program computes ephemerides of Sun, Moon, planets, comets, and stars using rigorous reduction methods from the _Astronomical Almanac_ and related sources. Includes PLAN404 series (see below) for positions of the planets, and a long-term extension of modern Lunar theory for the Moon's position. Reads ASCII file catalogues of stars and orbital elements. Displays all adjustments as it finds local azimuth and elevation, rise and set times, etc.
Ephemeris 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.
PyEphem provides scientific-grade astronomical computations for the Python programming language. Given a date and location on the Earth's surface, it can compute the positions of the Sun and Moon, of the planets and their moons, and of any asteroids, comets, or earth satellites whose orbital elements the user can provide. Additional functions are provided to compute the angular separation between two objects in the sky, to determine the constellation in which an object lies, and to find the times at which an object rises, transits, and sets on a particular day.
Skycalc is an interactive tool which conveniently handles the time-and-the-sky calculations commonly encountered in optical astronomy. It has many features useful for planning observations and at the telescope.