The Great Cluster in Hercules

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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By Jim Kaler. Return to STARS.