1938 – USA
‘Energy in stars is produced by hydrogen fusion reactions’
In nuclear fusion the nuclei of light atoms combine at very high temperatures and release enormous amounts of energy that is radiated from the surface of the star as heat and light.
An ordinary star is one of the simplest entities in nature; it is a sphere of gas that is by mass 73 percent hydrogen, 25 percent helium and 2 percent other elements. The temperature in the centre is high enough to fuse four nuclei of hydrogen together to form one helium nucleus.