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October 29, 2012

Perseus, the celestial hero, strides boldly across the northeastern sky on autumn evenings. The constellation stands close to the horizon as night falls, and high overhead in the hours after midnight. The figure is outlined by three streamers of stars that intersect at Perseus’s bellybutton — the constellation’s brightest star, Mirfak.

It doesn’t just look bright in our sky, though. Mirfak is one of the brightest stars in our region of the galaxy — thousands of times brighter than the Sun. That great brilliance makes the star easily visible across more than 550 light-years of space.

If you look around Mirfak, especially with binoculars, you’ll see a good sprinkling of fainter stars. Most of those stars are siblings of Mirfak — they’re all members of a cluster of about 150 to 200 stars. All of the stars in the cluster were born about 60 million years ago, from a single giant cloud of gas and dust.

One way astronomers deduce the birthday of the cluster’s stars is by looking at Mirfak, which is the cluster’s brightest and heaviest member. Such stars live relatively short lives, and Mirfak is getting close to the end of that lifespan. So the fact that it’s still around puts an upper limit on the age of the entire cluster.

While Mirfak is the brightest star in Perseus, it’s not the most famous. That honor goes to a star known as the demon — from a name that it shares with a villain from Batman. We’ll have more about that tomorrow.


Script by Damond Benningfield, Copyright 2012

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