1. GCSE Astronomy – Lesson 3
Nuclear Fusion
GCSE Astronomy – Lesson 3

2. Lesson outcomes Define nuclear fusion.
Describe and explain how the sun generates it’s energy.

4. Sun’s energy
The Sun consists of the elements primarily Hydrogen and Helium.
The Sun is both large enough and contains enough mass that the internal pressure at its centre (its core) is so hot (14 million °C) that it forces the nuclei of the hydrogen atoms to join together (to fuse) to make helium atoms in a process called the proton-proton chain.
A nuclear reaction (fusion) takes place and large amounts of light and heat are produced. 600 million tonnes of hydrogen are converted into 596 million tonnes of helium every second. The remaining four million tonnes gets converted into heat and light.

5. How does it work?
Nuclear fusion is where the nuclei of small atoms fuse together to form larger nuclei. This is how atoms are made. All atoms are created by the fusion of smaller atoms inside stars. When the star explodes these heavy atoms are dispersed into space. They may go on to form planets such as the Earth.
The most common fusion reaction inside our Sun is the fusion of hydrogen into helium.

6. The mass of the products of this reaction are slightly less than the mass of what we started with. The energy from the reaction comes from the conversion of mass into energy. The total mass of the Sun actually gets less by 400,000 tons a second. Despite this it has been calculated that the Sun will last for a few more billion years.
Teams of scientists across the world are working very hard on trying to recreate nuclear fusion on a reasonable scale in a fusion reactor.