The Outer & Inner Parts of the Sun

By Hayley Ames
The photosphere is the visible part of the sun.
4774344sean/iStock/Getty Images

The basic elements that make up the sun are the same as those that the Earth is formed from. The extreme heat of the sun, however, causes these materials to exist only in a gaseous state. The inner part of the sun has three layers: the energy-producing core, the radiative zone and the convection zone. The outer part of the sun, or the solar atmosphere, contains three layers: the photosphere, the chromosphere and the corona. Once the sun’s energy has reached the surface, it is released into space. Earth can then benefit from the light and heat that it produces.

The Core

The center of the sun is the first of three inner layers. The temperature of the sun’s core is about 15 million degrees Celsius (28 million degrees Fahrenheit). At this temperature, the structures of atoms are broken down. Nuclear fusion reactions that take place between these separated atomic particles as they collide with each other are the sun’s source of energy. These fusion reactions change hydrogen into helium, generating enormous volumes of energy.

The Radiative Zone

The second layer of the sun’s interior is called the radiative zone. It is in this area that the energy produced in the core is transported to the sun’s exterior, through radiation. The temperature in this area of the sun is around 5 million degrees Celsius (9 million degrees Fahrenheit). The energy is passed randomly among atoms, which store it temporarily and then release it for other atoms to absorb and pass on further until the gamma rays lose enough energy to become less harmful light energy. The process of energy transfer in the radiative zone is a very slow one, often taking more than 100,000 years to reach the next layer.

The Convection Zone

The final layer of the inner part of the sun is known as the convection zone. Here energy from the radiative zone travels to the outer part of the sun through a process of convection at temperatures of around 5,500 degrees Celsius (10,000 degrees Fahrenheit). In this zone, hot substances tend to rise to the surface and then sink down. When the material reaches the surface, it cools and falls back down to the bottom of the convection zone, causing it to circulate energy relatively fast in this layer. It takes around a week to travel from the bottom of the zone to the surface.

The Solar Atmosphere

Above the surface of the sun lies the solar atmosphere, the outer part of the sun. This can be divided into an additional three layers. The first of these layers is the one that can be seen through specialized telescopes. It has a similar appearance to a surface when it is viewed from far away, although the material here is still gaseous. Light energy is released into space from this layer. The chromosphere lies above the photosphere. This layer also emits light radiation. The temperatures of both of these layers are around 11,400 degrees Celsius (20,000 degrees Fahrenheit). But the temperature rises toward the top of this layer until it reaches the final outer layer, known as the corona, which reaches a temperature of around 1.7 million degrees Celsius (3 million degrees Fahrenheit). Here, magnetic fields create high temperatures in the gas that this layer is made up from. This is where ultraviolet rays are emitted from. The chromosphere and corona are only visible during a solar eclipse.

About the Author

Born in Norfolk, United Kingdom, Hayley Ames' writing experience includes blog articles for a travel website. Ames was awarded a Bachelor of Arts in English language and literature from the University of Sheffield in the United Kingdom.