" Star in a Box allows you to explore one of the most enigmatic tools in astronomy - the Hertzsprung-Russell diagram.
When you first open the box you start with a star with the same mass as
the Sun but you can change this to a different mass at any time. The
tracks that you see on the graph (on the left) map the lifecycle of the
star. You can play the animation of the star moving around the diagram,
and see how its brightness, size, surface temperature, and mass change
in the panels on the right.
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."