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Solar Interior

Major features of the Sun
The major features of the Sun. (Click for a larger image.) © UC Regents
The Sun is our nearest star. Its radiant energies light up our daytime sky and make all life possible on this planet, even from as far away as 93 million miles. Like many things in nature, the Sun consists of many different parts that influence each other and exchange both energy and matter.

Energy and Matter
Deep within the Sun's core where gravitational pressures compress and heat its gases, atoms collide so furiously that some fuse together. At temperatures of 15 million degrees Centigrade, its abundant store of hydrogen turns to helium via thermonuclear fusion. Every second, 600 million tons of matter are converted to pure, radiant energy. Some of this energy goes into creating pressure that literally holds up the Sun against gravity. The rest leaks out of the dense core in the form of light, and deposits huge amounts of energy throughout the inside of the star. It takes many thousands and possibly millions of years for this light energy to make it to the surface because there is so much matter in the way.

Like some enormous onion, the Sun's interior is a collection of regions with unique combinations of temperature, density and the manner in which energy moves through them. In a region that astronomers call the radiative zone, light is the most efficient medium to transport energy from deeper inside the Sun. The gas moves very little, and rotates in unison with the rest of the Sun as though it were a solid substance. While the gas temperatures plummet to only a few hundred thousand degrees Centigrade, light staggers to and fro until it gets about 1/3 of the way to the surface. The outer 1/3 of the Sun convects like a liquid in a boiling pot, because of a sharp change in the properties of the gas and its temperature. Astronomers can see these convection cells on the outer surface of the Sun, called the photosphere, which is the part that we see from Earth. The small cells are called granules, but they are in fact nearly as large as Earth and change their shapes in only a few minutes. Granules move about on top of larger 'super cells' which reach deep down into the interior of the Sun within the convective zone.

Other Stars
Stars much hotter than the Sun, such as Rigel or Deneb, have no convection zone at all, while stars much cooler than the Sun, such as Betelgeuse and Antares, have convective zones that reach almost to the cores of the stars. Because of the Sun's turbulent surface, many complex phenomena can occur on the surface as flows of charged particles cause magnetic fields, and these fields become entangled and amplified.

globe icon Find out more about the Sun-Earth Connection at the Sun-Earth Connection Education Forum Web site.

Text adapted from the Sun-Earth Connection Tutorial courtesy of NASA, originally written by Dr. Sten Odenwald. Images and videos courtesy of NASA unless otherwised noted.

Related to chapter 6 in the print guide.
Related Materials

Visit other pages in this section that focus on aspects of the Sun-Earth Connection.

The Solar Interior
Solar Cycle
Solar Flares
The Solar Wind
Plasma Clouds
Glossary Terms

Click for the definitions of the following words that are used on this page: (Definitions appear in a pop-up window.)

coronal mass ejection
geomagnetic field
geomagnetic storm
radiation belts
solar cycle
solar maximum
solar minimum
solar wind

View the full, printable version of the glossary.

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