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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