![]() To me, no globular cluster in the sky compares to 47 Tucanae. I find my eye drawn ever inward by the tight core as if on a treasure hunt. This energetic fizz of countless suns gradually diffuses outward from the cluster’s center into myriad streams of stars in eight prominent spidery arms, superimposed on a web of dimmer suns. It has a tight (3′-wide) yellowish core that sizzles like an Alka-Seltzer tablet in water. This is not the case with 47 Tucanae, whose form is the polar opposite. One’s gaze can seemingly rip through its core without difficulty, as if the cluster is laying bare all its secrets. An observer doesn’t have to work hard to resolve the starlight because it’s so spread out. It’s also “open,” with only a moderate concentration of stars in its core. Without question, Omega Centauri is a snow globe of glittering starlight. This is where the competition becomes tricky. The vote comes down to how the two clusters appear through the telescope - how they make you feel. On paper, we have a true competition, as both clusters have nearly the same values (including a magnitude 12.5 surface brightness for both). Let’s compare the two spectacles by the numbers: See Showdown 1 below (in gallery). Perhaps one of the best examples of how difficult it is to determine a clear-cut winner comes from impressions of the two most visually dynamic globular star clusters in the entire night sky: Omega Centauri (NGC 5139) and 47 Tucanae (NGC 104). Judging the visual appearance of globular clusters can become a matter of personal opinion, influenced by factors ranging from telescope size and magnification to one’s imagination or current mood. In some cases, the cluster’s apparent size also carried weight. But visual magnitude alone is not a good qualifier, so I also factored in the cluster’s horizontal branch (HB) magnitude - the rough magnitude you need to reasonably resolve the cluster - as well the magnitude of its brightest stars. I then ranked them in order of visual magnitude. I began by compiling a list of all the Messier (M) and New General Catalogue (NGC) globulars in each constellation visible within roughly 2 hours of right ascension on either side of the meridian in mid-August, and no further south than –45° declination. ![]() ![]() Among the brightest and best for northerners is the Hercules Cluster (M13), which British astronomer Thomas William Webb called the “finest of its class.”īut is it? You’ll find out in this August globular cluster showdown.įirst, let’s look at the criteria I used to make my picks. August evenings in the Northern Hemisphere are prime for seeking out globular star clusters. ![]()
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