Sirius

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If you turn up the flame on your outdoor gas grill, it burns hotter and brighter -- but it also drains the tank faster.

That's how things work for stars, too. As you increase a star's mass, it's like turning up the flame. The star burns hotter and brighter, but it flames out faster.

Consider Sirius, the brightest star in the night sky. It rises in the southeast in early evening, and climbs across the south during the night.

Sirius looks so bright in part because it's one of our closest neighbors -- less than nine light-years away; more about that tomorrow. But Sirius is also fairly bright in its own right. If you lined up Sirius and the Sun at the same distance, Sirius would look about 25 times brighter.

Sirius shines brighter because it's about twice as massive as the Sun. Heavier stars are squeezed tightly by their stronger gravity. That heats up their cores, which increases the rate of nuclear fusion -- the process that powers the stars. The stars produce more energy, so they shine brighter and hotter than stars with less mass.

Not surprisingly, though, if a star burns its fuel at a faster rate, it takes less time to use it all up.

Like the Sun, Sirius is "fusing" the hydrogen in its core to make helium. But while it'll take the Sun a total of 10 billion years or longer to use up its hydrogen, Sirius will burn through its hydrogen in about 2 billion years. So while Sirius lives a flashier life than the Sun, it'll live a shorter one, too.

Script by Damond Benningfield, Copyright 2008

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