NGC 5139, Omega Centauri, is the largest and most spectacular globular cluster in the night sky, and the largest and brightest in our galaxy. At 55 arcminutes, Omega Centauri is almost twice as large as the full moon in apparent size.

At magnitude 3.9, it is easily visible from a dark-sky observing site without a telescope as a fuzzy "star" in the constellation of Centaurus, hence its Bayer designation as Omega Centauri. It is located 15,000 light-years away from our Sun and contains 10 million stars in a diameter of 150 light-years. Omega Centauri is believed to be 12 billion years old, but it may have taken 2 billion years for the stars in it to form.

Omega Centauri is the largest of more than 200 known globular clusters in our galaxy. It is so large, with so many stars, that some astronomers think that is may be the core of a small dwarf galaxy that merged with the Milky Way.

The discovery of Omega Centauri was credited to Edmond Halley in 1677, but it was known to Ptolemy and Lacaille, and undoubtedly others as it is easily seen with the unaided eye. It was first recognized as a globular star cluster by John Herschel in the 1830's.

North is to the top in the above image.

NGC 5139 Catalogs: NGC 5139 Common Name: Omega Centauri Object Type: Globular Cluster Magnitude: 3.9v Size: 55' Constellation: Centaurus Image Field Centered At: RA: 13h 26m 47s Dec: -47° 29' 30"