GEOM is one of a number of programs dating from the Academia de Matemáticas Aplicadas of the Escuela Superior de Física y Matemáticas of the Instituto Politécnico Nacional in Mexico City. In its original form it was an adaptation of a program from the Quantum Chemistry Program Exchange whose purpose was to check the parameters in a molecular orbital program.
Since it was easy to exchange coordinates or merely mistype them, it was a useful precaution to make a crude drawing of the molecule to avoid gross errors in the placement of the atoms. From that time, the program has been gradually extended, using graphical techniques for families of spheres, so that now fairly complicated molecules can be shown in terms of rather elaborate spheres.
The same calculation which suppresses the back side of spheres and the portion of one sphere which lies within the interior of another can be repeated with another angular orientation to study the shadows cast by an infinitely distant point source of illumination. As such, it can be used to approximate the shadows cast during an eclipse, such as the one of local interest which occurred in the summer of 1991.