This is a RGB (red, green, blue) exposure of 10 minutes for each color taken with an SBIG STL-1301E CCD camera. The Kopernik 20-inch was working at around F/5.
Charles Messier (May 3rd, 1764): 'Nebula without star; center brilliant, gradually fading away; round. in a dark sky, visible in a telescope of 1-foot {focal length}. Plotted on chart of comet of 1779. (Diam. 3')'
W. Hershel: 'A beautiful cluster of stars about 5' or 6' diam.'
Burnham's Celestial Handbook: Large telescopes show an incredible swarm of countless star images, massing to a wonderful central blaze, with glittering streams of stars running out on all sides.
M-3, in the constellation of Canes Venatici, is a beautiful bright globular star cluster, certainly as splendid as any in the northern sky. Visually, it is similar to M-2 or M-15. It must contain a quarter of a million stars. Astronomers have studied M-3 intensively in order to estimate the age of clusters and the evolution of stars. Its age has been estimated as 5 billion years (Baade), and 11.4 billion years (Woolf). In 1958, Hoyle, using a computer to evaluate different theoretical models, and comparing the results with the observed color-magnitude diagram for this cluster, obtained an age of 6.5 billion years. There have also been several differing distance estimates, anywhere from 35 to 45 thousand light years. If M-3 is 40 thousand light years distant, its diameter is about 220 light years. (But Click here for the latest news on Globular Star Cluster distances and ages!!)
Globular star clusters contain some of the oldest stars known. However, it was shown by Sandage in 1953 that one unusual feature of M-3 is that it contains a very young, blue star of spectral type O8 (see also M-13). Since there is no sign of star formation in globular clusters, astronomers have been puzzled by the “blue cluster stars” for years. 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.
George Normandin, KAS
May 2nd, 2009