The globular cluster M15 is shown in this color image obtained with the Hubble telescope. Lying some 40,000 light-years from Earth in the constellation Pegasus, M15 is one of nearly 150 known globular clusters that form a vast halo surrounding our Milky Way galaxy. Each of these spherically shaped clusters contains hundreds of thousands of ancient stars. The stars in M15 and other globular clusters are estimated to be about 12 billion years old. They were among the first generations of stars to form in the Milky Way.