Rights: © Copyright 2014. University of Waikato. All Rights Reserved. Published 29 April 2014 Download

In this video, Associate Professor Bob Lloyd states that it is nuclear fusion that fuels the Sun. He then goes on to explain in simple terms how this process works by fusing lighter elements into heavier elements. By using Einstein’s famous equation E=mc2, he then explains why it is that so much energy is released.


Nuclear fusion is what happens in the Sun – it’s the combining of light elements into heavier elements to produce energy.

The Sun produces a large amount of energy by combining very light elements such as hydrogen to heavier elements such as helium and then lithium, oxygen, carbon, right up to iron. They combine because, once you get the nuclei sufficiently close together, there is a very strong attractive force called the nuclear force which holds them together.

The combination of the two masses is slightly less than the masses individually. So E=mc2, a very small change in mass will give you a very large change in energy because c is of course the velocity of light, which is 3 x 108 metres per second.

So normal nuclear power reactors are what’s called fission reactors – they split very heavy elements such as uranium into small bits and get energy. The Sun, however, works by combining very light nuclei such as hydrogen to make helium, and you also gain energy, but to get them that close is very, very difficult, and it needs extremely high temperatures, and that’s what you’ve got in the Sun.

Associate Professor Bob Lloyd, University of Otago, Department of Physics
Image of nuclear power plant, copyright d'archeos. Permission is granted to copy, distribute and/or modify this under the terms of the GNU Free Documentation License , Version 1.3 or any later version published by the Free Software Foundation and Creative Commons Licence 3.0
NASA/Goddard Space Flight Center