Creede Dark Skies: Omega Centauri

Omega Centauri is the name of a globular cluster in the southern constellation Centaurus. This cluster is the largest globular cluster in our Milky Way Galaxy. The number of stars (about 10 million), the mass (about 4 million solar masses), and the spectral distribution of stars support the hypothesis that this cluster is the remnant core of a dwarf galaxy captured by the Milky Way.

With a declination of -47.6° this cluster never rises more than 4.6° above the (sea-level) horizon at the latitude of Creede (37.8°). This is a problem, because our local horizon is mostly obscured by the surrounding mountain peaks and ridges. From my backyard observing location the view is blocked by the southern flank of Snowshoe Mountain and a neighbor's cabin. From the front yard, however, there is a view south toward Piedra Peak where I can watch this cluster glide just a couple degrees above the distant peaks.

Omega Centauri emerging from the southern flank of Snowshoe Mt, 08 May, 11:23pm MDT.

This image was obtained with a Canon FD 300mm f/4L lens and an Olympus E-M1iii camera (ISO 1600, 20 s) just as the cluster was transiting the meridian, its highest point in the sky. The sky brightness (near the zenith) was sqml=21.48.

Here is a closer look with a 1° field-of-view (ISO 1600, 60s):

Omega Centauri. E-M1iii + Canon FD 300mm f/4L. 2x binning.

Omega Centauri is an impressive sight in a small telescope or even binoculars. Here is a comparison to the "Great Hercules Cluster", M13:

M13 (left) and Omega Centauri (right). Canon FD 300mm f/4L.

The Hercules cluster M13 has about 500,000 stars, or roughly 1/20 as many as Omega Centauri. An interesting fact is that the total mass of all the stars in Omega Centauri is nearly the same as the mass of the supermassive black hole at the center of our galaxy. The Milky Way's central black hole has a radius less than half of the orbit of Mercury, while Omega Centauri spans about 150 ly.

Two years ago a waxing crescent moon lit up the sky as Omega Centauri emerged from behind Snowshoe Mountain. In the image below the silhouette of Piedra Peak is in the lower right corner, the bright rectangle near the bottom is a neighbor's cabin window.