Discovery Space: The Sun

The sun is the star central to both our planetary system and our lives as a huge power station providing the Earth with warmth and light. Its particle radiation generates the beautiful auroras (northern lights or southern lights) in the Earth’s atmosphere, but can also cause damage to electronics, satellites, and astronauts.

Anatomy of The Sun

The sun’s energy is generated by nuclear fusion. Its layered structure is similar to the layers of an onion. During a solar eclipse the sun’s outer gas layer, the chromosphere, becomes visible.

The sun is a sphere full of ionized gas in the form of hot plasma. The plasma contains mostly hydrogen, and then smaller quantities of helium and other heavier chemical elements. The atoms of these gases hit each other with great force because of the extremely high temperatures.

During this process, atomic nuclei and electrons are separated from each other. The sun comprises almost 99.9 percent of the total mass of the solar system. It has about 333,000 times the mass of the Earth, and 109 times the diameter.

The layered structure of the sun

The sun is held together by its own mass. This creates enormous pressure at the center, where the temperature is about 27 millionT (15 millionT). Due to the intensity of the heat, hydrogen nuclei move very quickly and can overcome their electrical repulsion to fuse together. Energy re- leased from this fusion reaction in the core is the energy we eventually receive on Earth. The solar core is surrounded by an extensive layer referred to as the radiative zone.

This is where the radiation from the core is projected back and forth between plasma particles in a process that can take up to a million years before finally passing through the radiative zone and reaching the next layer, the convection zone. Here, energy is transported to the surface of the sun by means of hot plasma movements, which cause the surface of the sun to appear to bubble. The convection zone is surrounded by the photo- sphere.

This layer is only a few hundred miles thick with a much cooler temperature of around 9900°F (5500°C). The photosphere emits the light that we can see on Earth. This layer is, therefore, often referred to as the sun’s surface, even though a star does not have a firm surface as such. The next layer up from the photo- sphere is the chromosphere.

Although the illumination from the photosphere normally overpowers this reddish shimmer, it can be observed for a few seconds during a solar eclipse. In the chromosphere, the temperature rises again to 18,000°F (10,000°C) while the particle density decreases significantly. The photosphere is enclosed by the corona which is visible during a solar eclipse in the form of an aureole of varying widths. The solar matter of this layer is very thin and gradually merges into interplanetary space.

In the corona, the temperature rises to about 3.6 million°F (two million°C) again. How the temperature is heated up to such a degree has not yet been explained, but a possible source of energy might be the sun’s magnetic field. Electrically charged particles are constantly released from the corona; it is these particles that are referred to as solar wind.


Stars like the sun mainly produce energy during a process called proton proton chain reaction. Hydrogen nude are positively charged protons When these protons fuse, a proton is con- verted into a neutron, and an atomic nucleus with two particles is produced

When this merges with another proton a nucleus of three particles is formed Finally these nuclei can go on to form a helium nucleus with two protons and two neutrons, releasing two of the original protons. Additional particles released during this chain of reactions include positrons, neutrinos, and very high-energy gamma rays.