"H" is for Hercules

A third of the way from Vega, the brightest star of summer, back to Arcturus, the brightest star of the spring sky, is an "H" shaped group of stars. This is the hero Hercules. He's upside down in the sky: the top (northern) two stars of the "H" represent his knees; the middle two, his waist, the stars at the bottom, his shoulders.

Just south of his western knee is the magnificent Hercules Cluster: hundreds of thousands of stars formed with our galaxy over ten billion years ago. It is one of a hundred or so globular clusters forming a spherical halo around the central hub of our galaxy.

Bright stars die young, so unlike new clusters like the Pleiades, the Hercules cluster has no bright stars: they all died long ago. Still, you can see this cluster as a compact, fuzzy ball of stars using only the simplest pair of binoculars.

When the universe was young, the only matter in existence was the simplest elements, hydrogen and helium, formed by the Big Bang. And so globular clusters, like the Hercules cluster, were formed by the condensation of this primordial material, and contain none of the heavier elements out of which planets are formed. The stars in this cluster have no planets, no life.

Stars first had to die, so that in titanic supernova explosions they could enrich the interstellar medium with the heavy atoms needed for planets and for life. Only second and third generation stars, like our own Sun, can have planets.

And maybe, just maybe, circling one of these stars is a planet just like Earth: a planet with life.

(04/23/08)