Globular clusters are gravitationally bound concentrations of approximately ten thousand to one million stars. They populate the halo or bulge of the Milky Way and other galaxies with a significant concentration toward the Galactic Center. Spectroscopic study of globular clusters shows that they are much lower in heavy element abundance than stars such as the Sun that form in the disks of galaxies. Thus, globular clusters are believed to be very old and formed from an earlier generation of stars . More recent estimates yield an age of 12 to 20 billion years; the best value for observation is perhaps 14 to 16 billion . Our galaxy has about 200 globular
clusters, most in highly eccentric orbits that take them far outside the
Milky Way. Most other galaxies have globular cluster systems as well, in
some cases (e.g., for M87)
containing several thousands of globulars! |
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M13 - Hercules This cluster shows up as a small grey blob in binoculars. I was disappointed with the view through the telescope as the cluster was still a grey blob. I couldn't resolve any stars at all, not even around the edges of the cluster. Increasing power didn't help either - just got a bigger gray blob. I'll keep trying. |
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Globular clusters have to be the most disappointing objects I've yet looked at through my 6" telescope. I've yet to look at these objects from a dark site, maybe this will help in seeing more detail in these objects. I hope to get to a dark site some time this winter. Using eyepieces of higher power did nothing to resolve individual stars in these clusters in fact the higher power made the object loose contrast and sharpness. I suspect that a larger telescope is required to resolve more detail in these objects. Update October 2000. Okay, I've now managed to see M13 when the sky has been pretty dark and what a difference it made to viewing this globular cluster. My faith in my equipment has been restored. I managed to get a clear night in October, Hercules was well down in the west where the sky was very murky and orange from light pollution. Despite this I managed to resolve stars for the first time in this globular and what a sight it was. The best description I can come up with is that it resembled looking into a bowl of sugar with a magnifying glass - it was very granular in appearance. There is more on the observing session here. Moral of the story - Make sure you are under dark skies if you want to resolve stars in this globular cluster. |
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