These graphs were produced with the aid of the SLALIB astronomical libraries, some custom code in Python, and GNUPLOT.
The SLALIB package is available at http://star-www.rl.ac.uk/. It provides very high precision astronomical libraries that are highly portable. In practice it is easier to use the Python pyephem package, which provides an interface to the slalib code.
GNUPLOT is a powerful library for producing graphs, and can handle much more complex cases than these. It can be found at http://www.gnuplot.info.