The Sun is getting brighter.

Not enough to notice, mind you. In fact, it’ll take more than a hundred thousand human lifetimes to tick up by even one percent. But that gradual change will add up. In a billion years or so, the extra energy should be enough to boil away Earth’s oceans and atmosphere, leaving nothing but a burned-out ball of rock.

The change is the result of changes deep inside the Sun.

Our star shines because its core is a giant nuclear reactor. It “fuses” lightweight hydrogen atoms to make heavier helium atoms — a process that produces enough energy to power the Sun.

As more hydrogen is converted to helium, the core shrinks and gets denser, which makes it hotter. And as the temperature goes up, so does the rate of nuclear reactions. That yields more energy, making the surface of the Sun brighter.

The Sun has already converted a large fraction of its hydrogen to helium. As a result, it beams about 25 percent more energy into space today than when it was born.

A billion years from now, it’ll shine about 10 percent brighter still — bright enough to heat Earth’s surface above the boiling point of water. And a few billion years after that, it’ll shine roughly twice as bright as when it was born.

By then, the Sun will have used up the hydrogen in its core, triggering changes that’ll make it shine hundreds of times brighter — a brilliant flare-up before it fades away for good.

More about the Sun tomorrow.
 

Script by Damond Benningfield

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