The Sun as a star

The Sun is a medium-sized star composed mostly of hydrogen and helium. It radiates energy into space as electromagnetic radiation.

The Sun emits radiation across a range of wavelengths. Most of its energy is emitted in three regions of the electromagnetic spectrum: infrared, visible light and ultraviolet. Visible light can be detected by the human eye. Infrared has longer wavelengths than visible light, while ultraviolet has shorter wavelengths.

Nuclear fusion in stars

Stars release energy through nuclear reactions in their cores. During a star’s stable phase, hydrogen nuclei join together to form helium nuclei. This process is called nuclear fusion.

The core is extremely hot, so hydrogen nuclei move rapidly enough for some to overcome their electrical repulsion and fuse. The helium formed has slightly less mass than the hydrogen nuclei involved. The difference in mass is released as energy.

Energy from fusion travels from the core towards the star’s surface. It ultimately contributes to the energy the star radiates into space. The Sun is a star powered by these fusion reactions.