The Sun as a Star (Cambridge (CIE) IGCSE Physics): Revision Note

The Sun as a star

• The Sun is a medium-sized star which lies at the centre of the Solar System

• It consists mostly of the two elements hydrogen and helium

• It radiates most of its energy in the infrared, visible and ultraviolet regions of the electromagnetic spectrum

Nuclear fusion in stars

Extended Tier Only

• Stars are huge balls of (mostly) hydrogen gas

• In the centre of a star, hydrogen nuclei undergo nuclear fusion (opens in a new tab) to form helium nuclei

• An equation for a possible fusion reaction is:

${}_1{}^2\mathrm{H}+{}_1{}^3\mathrm{H}\to {}_2{}^4\mathrm{He}+{}_0{}^1\mathrm{n}$

• Where ${}_1{}^2\mathrm{H}$ (deuterium) and ${}_1{}^3\mathrm{H}$ (tritium) are both isotopes of hydrogen

  • These are formed through other fusion reactions in the star

• A huge amount of energy is released in the reaction

• All stable stars are powered by nuclear fusion reactions