|Though 25,000 light years away, the great globular cluster Messier 13 in Hercules is still visible to the naked eye. Some 12 billion years old, this massive system contains half a million or so solar masses `packed into a volume only 100 light years across. Born before the Galaxy's stars had a chance to create metals and distribute them them in star-forming regions, M 13's iron content relative to hydrogen is just 5 percent that of the Sun. Omega Centauri and 47 Tucanae, seen in context in their constellations, are even brighter and more massive. University of Illinois Prairie Observatory.|
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