Current astronomical evidence suggests that some globular clusters may have been the oldest stellar collections to form early in the history of the universe. By studying the color-magnitude diagrams of globular clusters, astronomers have concluded that some of them are at least twelve billion years old, which is as old as the most distant galaxies yet observed. Interestingly, some globular clusters have been shown to contain stars with a wide range of ages. Astronomers are carefully studying formation and evolutionary history of these clusters to learn about the cosmos when it was young.