StarDate: July 26, 2009

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Giants lumber boldly across the sky on July and August evenings. They're some of the biggest, brightest stars in the galaxy. And some of them face giant deaths -- they'll blast themselves to bits.

Giants actually represent only a tiny fraction of the total number of stars in the galaxy. But most "average" stars are too small and faint to see unless they're really close by. Giants, on the other hand, are so bright that they're clearly visible across dozens, hundreds, or even thousands of light-years.

When astronomers call a star a giant, they're not just talking about its size. They're also describing its place in its lifecycle.

Normal giants are old stars that have puffed up as they near the ends of their lives. They'll soon shed their outer layers, leaving only their dense cores -- white-hot balls known as white dwarfs.

A prime example is Arcturus, the leading light of Bootes, the herdsman. This bright yellow-orange star is high in the west at nightfall and sets a few hours later.

Some other stars are supergiants. These stars are bigger and heavier than ordinary giants. Some good examples include Antares, the "heart" of Scorpius, which is due south in early evening; and Spica, the brightest star of Virgo, in the southwest. When these stars die, they'll go out with displays befitting a giant: They'll explode with titanic force, shining as brightly as billions of normal stars.

We'll have more about Antares tomorrow.

Script by Damond Benningfield, Copyright 2002, 2006, 2009

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