Shop Windows to the Universe

Check out the fun Earth science related bumper stickers in our online store! Express yourself!
The Sun's radiative zone lies between the incredibly hot core and the outer convective zone.
Click on image for full size

The Sun's Radiative Zone

The Sun's radiative zone is the section of the solar interior between the innermost core and the outer convective zone. In the radiative zone, energy generated by nuclear fusion in the core moves outward as electromagnetic radiation. In other words, the energy is conveyed by photons. When the energy reaches the top of the radiative zone, it begins to move in a different fashion in the convective zone. In the convective zone, heat and energy are carried outward along with matter in swirling flows called convection cells. This motion is similar to the roiling flows seen in a pot of boiling water.

The inner parts of the Sun (core and radiative zone) spin differently than the outer layers (convective zone). The boundary between these two types of rotation, which lies between the radiative and convective zones, is called the tachocline.

Many other stars also have radiative zones. The Sun's radiative zone extends from the core outward to about 70% of the Sun's radius. In a smaller (than the Sun) star that is cooler than our Sun, the convective zone tends to be larger, extending deeper into the star's interior. Thus the radiative zone tends to be smaller. In very small, cool stars the convective zone may reach all the way to the star's core, and there may be no radiative zone at all. In a larger (than the Sun) star with a higher temperature, the radiative zone tends to be larger and the convective zone smaller. Especially large, hot stars may not have a convective zone at all - their radiative zone may extend all the way from the core to the star's surface.

Last modified August 23, 2005 by Randy Russell.

Shop Windows to the Universe Science Store!

Cool It! is the new card game from the Union of Concerned Scientists that teaches kids about the choices we have when it comes to climate change—and how policy and technology decisions made today will matter. Cool It! is available in our online store.

Windows to the Universe Community



You might also be interested in:

The Solar Interior

To understand how our Sun works, it helps to imagine that the interior of the Sun is made up of different layers, one inside the other. The innermost layer, the solar core, is the region where the energy...more

The Convection Zone

The convection zone in the Sun occurs above the radiative zone, at about .7 to .8 solar radii from the center of the Sun. At this point the temperature gradient (the change in temperature with depth)...more

Fusion Reactions

Nuclear fusion is a process where two or more nuclei combine to form an element with a higher atomic number (more protons in the nucleus). Fusion is the reverse process of nuclear fission. Fusion of light...more

The Sun and the Solar Atmosphere

What are the "parts" of the Sun? The photosphere, the visible "surface" of the Sun, defines the outermost boundary of the "inside" of the Sun. The three main regions of the...more

The Sun's Radiative Zone

The Sun's radiative zone is the section of the solar interior between the innermost core and the outer convective zone. In the radiative zone, energy generated by nuclear fusion in the core moves outward...more


IMF stands for Interplanetary Magnetic Field. It is another name for the Sun's magnetic field. The Sun's magnetic field is enormous and is carried by the solar wind. The solar wind and magnetic field are...more

The Hydrogen Fusion Process

The basic Hydrogen fusion cycle involves four Hydrogen nuclei (protons) and two electrons and yields a Helium nucleus, two neutrinos and six photons. This process occurs in three steps: the first one is...more

Fusion Inside the Stars

Fusion in the core of the stars is achieved when the density and temperature arising from the gravitational pressure are high enough. There are different fusion cycles that occur in different phases of...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA