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What is the Sun made of?

The Sun is a huge, glowing sphere of hot gas. Most of this gas is hydrogen (about 70%) and helium (about 28%). Carbon, nitrogen and oxygen make up 1.5% and the other 0.5% is made up of small amounts of many other elements such as neon, iron, silicon, magnesium and sulfur. The Sun shines because it is turning hydrogen into helium via the process of nuclear fusion in its extremely hot core. This means that as time goes on, the Sun has less hydrogen and more helium. For more about nuclear fusion and how the Sun shines, see Spitzer's IRrelevant Astronomy video Fission vs. Fusion.