Moon and Regulus

StarDate: April 5, 2009

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A star that's nearing the end of "middle age" huddles close to the Moon tonight. It's already one of the brightest stars in the night sky. But as it moves into the final stages of life, it'll get a lot brighter.

The star is Regulus, the "heart" of Leo, the lion. It's above the Moon as night falls.

For the last 250 million years or so, Regulus has been steadily "burning" through the hydrogen in its core. It's not like the flame on your kitchen stove, though. Instead, it's nuclear burning -- a process that combines the nuclei of hydrogen atoms to make helium.

The same thing is happening in the core of the Sun -- and has been for four and a half billion years.

Regulus is much younger than the Sun, but it's also about three and a half times heavier. The extra mass squeezes its core more tightly, making it much hotter. And just as turning up the thermostat uses up your heating oil more quickly, turning up the heat in a star's core causes it to use up its hydrogen more quickly.

As it finishes the hydrogen, the core will shrink and get even hotter -- hot enough to start burning its helium to make even heavier elements.

The hotter core will produce more radiation, puffing up the star's outer layers. Eventually, Regulus will swell to dozens of times its current size, and shine dozens of times brighter. For a few million years, it will become a stellar giant -- giving the mighty lion an even bigger heart.

Script by Damond Benningfield, Copyright 2009

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