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Our Changing Star

November 5, 2021

Our star — the Sun — is quite impressive. Its size, mass, and brightness place it among the top 10 percent of all the stars in the galaxy. And it’ll get even more impressive in the future. It’s getting bigger and brighter — all while losing mass.

The Sun shines by “fusing” atoms of hydrogen in its core to make helium. Currently, it fuses almost 700 million tons of hydrogen every second. Not all of the hydrogen is turned into helium, though. Seven-tenths of one percent is converted to energy, which radiates into space, making the Sun shine. Over the Sun’s four-and-a-half-billion-year lifetime, enough matter has been converted to energy to make almost a hundred Earths.

As the helium in the core builds up, the core shrinks. Hydrogen in a layer outside the helium is pulled inward. It gets hotter, revving up the reactions. The hotter core heats the Sun’s outer layers, causing them to expand. So today, the Sun is about 15 percent wider, and 50 percent brighter, than when it was born.

That process will continue. In a billion years or so, the Sun will be so bright and hot that it will boil away Earth’s oceans — turning our planet into a burned-out cinder.

And about five billion years from now, the Sun will begin fusing the helium to make other elements. That will make the Sun much wider than it is today. It might get big enough to engulf anything that remains of Earth — a planet consumed by its impressive star.

Script by Damond Benningfield

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