Omega Centauri (w Cen; NGC 5139)

A particularly bright globular cluster of stars in the southern constellation Centaurus. Its diameter, 620 light years, is the largest of any globular cluster known. Omega Centauri lies at a distance of 16,500 light years. Through a large telescope, it is seen to spread over as much as 1° of the sky. Its total magnitude is 3.6 and it is easily visible to the naked eye. A curious feature is its shape, which is distinctly elliptical with axes in the ratio 5:4. The name Omega Centauri is of a type normally given to single stars. The cluster was mistaken for a single star by early observers at Mediterranean latitudes, for whom it never rises more than about 10° above the horizon.