4.1b Interior of the Sun

What does the sun look like?

Different instruments pick up different features of the sun. None can show us the sun’s interior. But studies from the SOHO spacecraft and other craft allow us to study the interior. We know a surprising amount about a body that is so hot and so far away.

Layers of the Sun

The sun is made almost entirely of the elements hydrogen and helium. The sun has no solid material. Most atoms in the sun exist as plasma . Plasma is superheated gas with an electrical charge. Because the sun is made of gases, it does not have a defined outer boundary. Like Earth, the Sun has an internal structure. The inner three layers make up what we would actually call “the sun.”

Internal Structure

Because the sun is not solid, it does not have a defined outer boundary. It does, however, have a definite internal structure with identifiable layers ( Figure below ). Since the layers are not solid, the boundaries are fuzzy and indistinct. From inward to outward, the layers are: the core, the radiative zone, and the convection zone.

The layers of the Sun.

The Core

The core is the sun’s innermost layer. The core is plasma. It has a temperature of around 15 million degrees Celsius (°C). Nuclear fusion reactions create the immense temperature. In these reactions, hydrogen atoms fuse to form helium. This releases vast amounts of energy. The energy moves toward the outer layers of the sun. Energy from the sun’s core powers most of the solar system.

Radiative Zone

The radiative zone is the next layer out. It has a temperature of about 4 million degrees °C. Energy from the core travels through the radiative zone. The energy travels at an extremely slow rate. Light particles are called photons . In the radiative zone, photons can only travel a few millimeters before they hit another particle. The particles are absorbed and then released again. It may take 50 million years for a photon to travel all the way through the radiative zone.

The Convection Zone

The convection zone surrounds the radiative zone. In the convection zone, hot material from near the sun’s center rises. This material cools at the surface and then plunges back downward. The material then receives more heat from the radiative zone. The first video describes the basics of our sun, including how it is powered by nuclear reactions: http://www.youtube.com/watch?v=JHf3dG0Bx7I (8:34).

The second video discusses what powers the Sun, and what is its influence on Earth and the rest of the solar system: http://www.youtube.com/watch?v=S6VRKKh6gyA (8:25).


  • convection zone : Layer of the sun that surrounds the radiative zone whereenergy moves as flowing cells of gas.
  • core : Extremely hot center of the sun where nuclear fusion takes place.
  • photon : Light particle.
  • plasma : High energy, high temperature form of matter; electrons are removed from atoms, leaving each atom with a positive electrical charge.
  • radiative zone : Layer of the sun immediately surrounding the core; energy moves atom to atom.


  • The sun is made mostly of plasma. Plasma is superheated gas with a positive electrical charge.
  • Nuclear fusion takes place in the sun’s extremely hot core.
  • The radiative zone is outside the core.
  • The convection zone is where convection takes place. It is located outward from the radiative zone.


Use the resource below to answer the questions that follow.

  1. How much of the mass of the solar system is in the sun?
  2. What is the sun’s surface temperature?
  3. What is the sun’s core temperature?
  4. Explain what happens in the core of the sun.
  5. How long does it take for photons to escape the sun?


  1. What are the properties of the core?
  2. What is plasma?
  3. What powers the sun?

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )


Connecting to %s