The Sun is the source of almost all our energy. It is a huge ball of hot gases that gives off energy as heat and light. This is called solar energy, which just means energy from the Sun. The amount of energy produced by the Sun every second is a 100 billion times more than the largest coal-fired power station in Europe.

Nuclear fusion

Nuclear fusion is the term used by scientists to describe the process occurring in the Sun that causes the release of energy.

Nuclear fusion occurs in the core area or centre of the Sun. Here, temperatures are around 15,000,000°C. Gravity pulls all of the mass of the Sun inwards, creating pressure so intense that nuclear reactions take place. The nuclei of hydrogen atoms smash together and fuse to form larger atoms such as helium nuclei. The mass of each new helium nucleus is slightly less than the total mass of the four original hydrogen nuclei required to produce it. The difference in the mass is converted into vast amounts of energy.

The energy released in nuclear fusion is equivalent to 100 billion H-bombs every second. It is interesting to note that the energy released is described by Albert Einstein’s famous equation E=mc2 where E is energy, m is mass and c is the speed of light (which is as fast as 7½ times around the world in 1 second!).

The Sun’s energy eventually reaches the Sun’s surface – though it can take a million years to do so.

The Sun’s radiation – the electromagnetic spectrum

When the energy produced by these nuclear reactions reaches the Sun's surface, it is radiated out into space. Scientists have identified this energy as a spectrum of many different wavelengths of electromagnetic rays. They have called this the electromagnetic spectrum. Scientists have classified the various wavelengths within the electromagnetic spectrum into 7 different groups. One group is called visible light and it includes all the colours we can see. Other wavelengths are too long or too short to be seen by the human eye.

Streams of tiny charged particles such as electrons and protons are also radiated out from the Sun. These streams of particles are known as solar wind. High-energy particles within solar wind are often referred to as solar cosmic rays. The Earth’s atmosphere blocks out certain wavelengths of radiation that would be harmful to life. This includes cosmic rays, X-rays and nearly all ultraviolet light.

The small amount of radiation that reaches the Earth is visible light (which we call sunlight), infrared light (which produces heat in things that it reaches), a small amount of ultraviolet light and short radio waves. Although we only get a small amount of the Sun’s radiation, more energy hits the Earth in 1 hour than is used by all human activity of the entire population of the Earth in 1 year. 

Read about the different types of radiation.

Nature of science

Where possible, scientists try to find natural ways to classify things. Radiation from the Sun is classified according to wavelengths and frequency of rays. Rays have been classified into 7 groups of similar sized wavelengths and frequencies. Scientists need to group or classify things in order to study them.

    Published 9 August 2010