Globular Star Cluster M-13 (NGC 6205)

Globular Cluster, M-13
An image taken with a Canon D40 DSLR camera thru our 20-inch telescope.

Description of M-13 in The Deep Sky Field Guide to Uranometria 2000 (c) Willmann-Bell, Inc.:

Globular Cluster M-13 is perhaps the best known deep sky object in the summer sky. It is just visible to the unaided eye under very dark conditions. It’s bright stars and rather loose structure has made it a favorite target of both amateur and professional astronomers. Although it is a fine object in the smallest of telescopes, views of M-13, like those of other globular clusters, greatly improve with each increase in telescope size. In 1979 Dr. R. Griffin had the lucky chance to observe it visually through the 200 inch Palomar Telescope, and described the view as ‘rather like looking into a bowl of sugar!’

The cluster was discovered in 1714 by Edmond Halley (of Halley’s Comet fame). However, in the primitive telescopes of early observers like Halley and Charles Messier, M-13 was not resolvable into stars. W. Hershel, in the last part of the 18th century, seems to be the first to recognize M-13 to be a star cluster. He thought that it consisted of about 14,000 stars, but astronomers now estimate that there are a half million stars in the cluster, contained within a sphere of about 100 light years diameter. Current estimates place M-13 at a distance of 25,000 light years, with an age of 14 billion years. (But Click here for the latest news on Globular Star Cluster distances and ages!!)

Globular star clusters contain some the oldest stars known. However, strangely, M-13 and other globulars each contain a few blue giants, which are typically very young stars. Since there is no sign of star formation in globular clusters, astronomers have been puzzled by the “blue cluster stars” for years. However, recent observation and theory suggests that the blue giants in globular clusters are the result of the merging of two old stars, and are not recently formed young stars.