The original implementation of this calendar was produced in 1975 hand drawn on brown wrapping paper. Another version was drawn on a drum plotter driven by an IBM 1130 running an ephemeris coded on punched cards in FORTRAN. Both of these showed the new, full, and quarter moons, and the quarter moons were drawn backwards, as was only noticed and reported by Joan's father. The illuminated limb, the circular, lit edge of the moon, is always closer to the sun than the dark limb. This original calendar was printed in the college printshop in black on grey, hand colored with white pencil, and sold in the cafeteria.

Another version was produced around 1999 using an ephemeris coded in C and loaded into Tcl/Tk as an extension.

The current version is an exercise in open standards browser programming. All the computations for the calendar are performed in your browser in Ecmascript, the standardization of Javascript by ECMA. The graphical depiction of the calendar is done using SVG, the structured vector graphics language defined by the World Wide Web Consortium.

The javascript sources for the Moons calendar consist of emphemerides.js for computing the positions of the sun, moon, and planets, ephemimages.js for computing the moon image painted for each phase, parse_search.js for handling the parsing of the window.location.search string to fetch parameters, and generate.js to organize the calculations and produce the SVG graphics for the calendar.

The ephemeris is taken from Paul Schlyter's low precision ephemeris, where you should go for a more detailed explanation. This computation is good to 1-2 arc minutes accuracy, and that accuracy is good for some period of years around 2000.