The celestial scorpion skitters low across the southwestern sky
the next few weeks. In fact, it's so low that its tail barely
clears the horizon. The star that marks the junction between
Scorpius's tail and the body doesn't look special at all. It's
known as Zeta Scorpii. Binoculars reveal that it's really two
stars, not one. They're not related, though. Zeta-2 is about 150
light-years away, while Zeta-1 is many times farther -- up to
six thousand light-years. That means that while Zeta-1 looks
puny, it's actually one of the most impressive stars in the
galaxy. Zeta-1 is a supergiant. It's about 60 times as massive
as the Sun. Because of that great heft, it burns through the
nuclear fuel in its core in a hurry. All of that energy heats
its outer layers to tens of thousands of degrees. And the
combination of its size and temperature makes it extremely
bright: If you add up all of its energy -- the light we see,
plus other forms of energy we can't see -- Zeta-1 is probably a
million times brighter than the Sun.