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Narrator: In this demonstration

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you'll use balls of clay to explore how stars fuse elements inside their

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cores. Each different color represents a different element. Here,

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pink represents hydrogen, blue is helium,

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purple is carbon, orange

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is oxygen, and this tennis ball is neon.

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We'll start with hydrogen just like you've in the center of a

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young star. The inside of a star is hot and dense and all of these

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hydrogen atoms keep bumping together. Often, some of them will stick

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together, this is called fusion.

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So we squish together four pink balls representing

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hydrogen and these form a new element--helium--represented by the blue clay.

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The sun's been doing this for nearly five billion years.

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Eventually the hydrogen in the center of the star runs low and we've mostly got

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a lot of helium jostling together instead. When hydrogen fusion

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stops the star is no longer in equilibrium and the core shrinks down.

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But this makes things even hotter so the star can start to fuse helium into

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carbon. So we squish together three blue helium atoms to make one

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purple carbon atom. In the sun this

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is where things will end once the helium runs low. But if a star is

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much bigger than the sun, the core will shrink again and it will get even hotter at the center.

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Now the star can fuse together a carbon and a helium atom creating

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oxygen. So we'll squish a blue helium atom and a purple carbon

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atom and that turns into one orange oxygen atom. You can

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imagine what happens when the oxygen runs low and fusion stops once more.

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The core shrinks, things get hotter, a new fusion can begin again,

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helium an oxygen start to fuse into neon. So we squish

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a blue helium atom and an orange oxygen atom, and swap that out for a

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tennis ball that represents neon. Depending on the size of the star

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this process can continue through the periodic table up to the point where iron is formed.

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But to fuse iron you need to input energy. With energy going

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into fusion instead of coming out of it, the star can never be in equilibrium

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again and its day are numbered.

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