  The paper presents an interactive module created through the Wolfram
Demonstrations Project that visualizes the Zeeman effect for the small magnetic
field strengths present in the interstellar medium. The paper provides an
overview of spectral lines and a few examples of strong and weak Zeeman
splitting before discussing the module in depth. Student discovery is aided
with example situations to investigate using the interactive module, which is
targeted at the upper undergraduate or early graduate level. This module
(http://demonstrations.wolfram.com/TheZeemanEffectInTheInterstellarMedium),
which uses free software, can be used in classroom activities or as a means of
introducing students to the Wolfram Demonstrations Project as a learning
resource.
