Located in the constellation Hercules, this globular cluster is about 200 light years in diameter. Because the stars in a globular cluster are believed to form from a single cloud of gas at nearly the same time, all are roughly the same age and have the same composition. Differences among them are probably a function of their mass. Thus globular clusters have been instrumental in determining how mass affects stellar evolution. 
    Stars create energy through nuclear fusion. The rate of fusion depends on a star’s mass; a star with greater mass will burn its fuel more quickly than one that is lighter. So stars with greater mass have shorter lifetimes. They either consume the hydrogen in their