Cosmic rays, despite having been studied for more than a century, are still an important
source of knowledge about the Universe, yet they are far less familiar to a wider audience
than other fields of physics. For this reason the Czech Particle Physics Project (CPPP) has
developed a new interactive educational tool that can be used in masterclasses to teach high
school students about cosmic rays, and that is equally suitable for the general public. It has
been prepared in cooperation with the Cosmic Ray Extremely Distributed Observatory (CREDO), a
collaboration dedicated to the observation and study of cosmic rays on a global scale. The
module contains a basic introduction to the topic and an interactive part that simulates
cosmic-ray observatories based on detector arrays. Its goals are to teach students what cosmic
rays are, what their production sources are, how they can be observed, and how some of their
properties are studied. Through the process of manual event classification and the procedure of
fitting a function to data points, students are introduced to the concepts of background, the
chi-squared test, and other methods of analysis used in real scientific studies. The results
produced by the user are presented in the form of skymaps in different celestial coordinate
systems that illustrate the basic principles of astronomical observations. The module is
accessible at \href{http://cern.ch/cppp}{http://cern.ch/cppp}.