“The sun is a miasma
Of incandescent plasma
The sun’s not simply made out of gas
No, no, no
The sun is a quagmire
It’s not made of fire
Forget what you’ve been told in the past” -They Might Be Giants
Ask anyone where the Sun (or any star) gets its energy from, and most people will correctly answer “nuclear fusion.” But if you ask what’s getting fused, most people — including most scientists — will tell you that the Sun fuses hydrogen into helium, and that’s what powers it. It’s true that the Sun uses hydrogen as its initial fuel, and that helium-4 is indeed the end product, but the individual reactions that take place to turn hydrogen into helium are surprisingly diverse and intricate.
There are actually four major reactions that take place in the Sun: fusing two protons into deuterium, fusing deuterium and a proton into helium-3, fusing two helium-3 nuclei into helium-4, and fusing helium-3 and helium-4 in a chain reaction to produce two helium-4 nuclei. Note that only one of those reactions actually turns hydrogen into helium, and that’s not what makes up either the majority of reactions or the majority of the Sun’s energy!