M15 is a globular cluster of stars in the constellation Pegasus. It is perhaps the densest of all the globular clusters in the Milky Way. It is also the only known globular cluster to contain a planetary nebula. M15 contains over 100 variable stars which ranks it third for variables. It also contains 9 known pulsars. This cluster is 40,000 light years distant, and with a visual magnitude of 6.2.