The Keystone 
You can never judge a star by its appearance alone. The four stars at the center of Hercules, for example, all look pretty much alike. But each has its own story that’s different from all the others.
The stars form a sort of lopsided square called the Keystone. It’s well up in the east at nightfall.
Its brightest star, at the upper right, is Zeta Herculis. Moving clockwise, the other three are Epsilon, Pi, and Eta Herculis.
Zeta is the closest of the four, at a distance of just 35 light-years. It actually consists of two stars. One of them is bigger, heavier, and brighter than the Sun, while the other is smaller, lighter, and fainter. The larger one is nearing the end of its life, so it’s undergoing some changes that have caused it to puff up and shine brighter.
Epsilon is also a binary, although both of its stars are more impressive than the Sun. But like the Sun, they’re both in the stellar equivalent of middle age, steadily “burning” through the hydrogen in their cores.
Pi is the most impressive member of the Keystone. It’s about 370 light-years away — more than 10 times farther than Zeta. It’s so large that it would just about fill the orbit of Mercury, the closest planet to the Sun. And even though it’s just a small fraction of the Sun’s age, it won’t live much longer.
And finally, Eta is also more impressive than the Sun. And it, too, is nearing the end of its life — a stage the Sun won’t enter for billions of years.
Script by Damond Benningfield, Copyright 2012