Zeta Ophiuchi

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The stars definitely are not equal. They have different masses, which means they have different temperatures and colors. The heaviest stars shine brightest, and some of them shine hottest, too. Astronomers designate these stars as class O.

Such stars are rare. For one thing, the universe doesn't make many of them. For another, O-type stars don't live long. They burn through their fuel in a hurry, and die within a few million years of their birth. By comparison, the Sun has been shining for four and a half billion years.

But you can see one class O star tonight. It's Zeta Ophiuchi, in the large constellation Ophiuchus, the serpent bearer. It's about 460 light-years away, and it's about 20 times as massive as the Sun.

Zeta Ophiuchi is extremely bright. It emits as much visible light every minute as the Sun produces in three days. But the star is much hotter than the Sun, too. As a result, most of its energy is in the form of ultraviolet radiation. When you add that in, Zeta Ophiuchi is thousands of times brighter than the Sun.

Because they're so hot, O stars shine blue. But Zeta Ophiuchi doesn't look blue. That's because it's behind some dust that dims and reddens its light. In fact, if the dust weren't there, Zeta Ophiuchi would be one of the 25 brightest stars in the night sky.

Zeta Ophiuchi will pay a price for its luster, though. Millions of years from now, it'll explode as a supernova -- while the more modest Sun shines on.

Script by Ken Croswell, Copyright 2008

For more skywatching tips, astronomy news, and much more, read StarDate magazine.