Omega Centauri globular star cluster. True-colour optical image of the globular star cluster Omega Centauri (NGC 5139). This is one of the largest and brightest globular clusters in our galaxy. It lies around 16,500 light years away in the constellation Centaurus. It is thought to be around 620 light years in diameter, and contains over a million stars. Globular clusters tend to be very old, and at 10,000 million years old, this is one of the oldest known. Omega Centauri is one of the many globular clusters which form a spherical halo around our galaxy. This image was produced by digitally combining photographs taken by the UK Schmidt Telescope in blue and red light.