Explore one of the most enigmatic tools in astronomy, the Hertzsprung-Russell diagram, interactively with your students. Stars can take billions of years to go through their lives with the dramatic events taking place in relatively short periods of time. In the animation we speed up time when the star is not really changing much and slow things down for the dramatic phases of the star's life. Students can play the animation of the star moving around the diagram, and see how its brightness, size, surface temperature, and mass change over time.