Omega Centauri is one of the few globular clusters visible to the naked eye. It appears almost as large as the full Moon when seen from a dark, rural area. It is the brightest, largest and, at 4 million solar masses, the most massive known globular cluster in the Milky Way. Of all the globular clusters in the Local Group of galaxies, only Mayall II (orbiting the Andromeda Galaxy) is brighter and more massive. Orbiting through the Milky Way, Omega Centauri contains several million Population II stars and is about 12 billion years old.