the sun, which consists primarily of hydrogen and helium, is fueled by nuclear energy stored in the bonds that hold nuclei together. It is released as radiation when hydrogen nuclei fuse together to form helium nuclei. This is called nuclear fusion and is the fundamental physical mechanism for how the sun shines, providing us energy in the form of the light and heat that gave rise to all life on the planet. It remains the sole source of energy for all life on Earth, except for us over the past few thousand years since we discovered its power stored in fossil fuels.
