The stars that are visible to the naked eye are all different, but most of them share a few general characteristics. Most are brighter and more massive than the Sun, for example. Many are also younger than the Sun. Paradoxically, though, they're also closer to the ends of their lives.
One example is a star known as Gienah. It's the brightest star of the faint but distinctive constellation Corvus, the crow, whose four main stars form a pattern that looks a bit like a sail. It's low in the southeast at nightfall and glides across the south during the night.
Although Gienah doesn't look all that impressive, it's actually about 350 times brighter than the Sun. That's because it's about four times as massive as the Sun. Heavier stars must "burn" the hydrogen in their cores more quickly to generate enough energy to keep themselves from collapsing. That extra energy makes them shine much brighter.
But because they consume their hydrogen so much more quickly, heavier stars also "age" more quickly than slimmer ones. So even though Gienah is only about a quarter of a billion years old -- a few percent of the age of the Sun -- it's nearing the end of its "normal" lifetime. Within a few million years it'll begin to enter the final stages of life. It'll puff up to many times its current size, then cast its outer layers into space, leaving behind only its hot but tiny core.
We'll talk about another star in Corvus that's already going through that process tomorrow.
Script by Damond Benningfield, Copyright 2011
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