Layers of the Sun

The Sun, with layers labeled: Core, radiative zone, Convection zone, chromosphere, and corona. Features, including a solar prominent, subsurface flows, sunspots, flare, and a corona hole are labeled.
The Sun is a dynamic star, constantly changing and sending energy out into space. By studying our Sun, scientists can better understand the workings of distant stars. Credits: NASA

The Sun and its atmosphere consist of several zones or layers. From the inside out, the solar interior consists of:

  • The Core – the central region where nuclear reactions consume hydrogen to form helium. These reactions release the energy that ultimately leaves the surface as visible light.
  • The Radiative Zone – extends outward from the outer edge of the core to base of the convection zone, characterized by the method of energy transport – radiation.
  • The Convection Zone – the outermost layer of the solar interior extending from a depth of about 200,000 km to the visible surface where its motion is seen as granules and supergranules.

The solar atmosphere is made up of:

  • The Photosphere – the visible surface of the Sun.
  • The Chromosphere – an irregular layer above the photosphere where the temperature rises from 6000°C to about 20,000°C.
  • A Transition Region – a thin and very irregular layer of the Sun’s atmosphere that separates the hot corona from the much cooler chromosphere.
  • The Corona – the Sun’s outer atmosphere.

Beyond the corona is the solar wind, which is actually an outward flow of coronal gas. The Sun’s magnetic fields rise through the convection zone and erupt through the photosphere into the chromosphere and corona. The eruptions lead to solar activity, which includes such phenomena as sunspots, flares, prominences, and coronal mass ejections.

This infographic labels the parts of the Sun (from most inward to outward): Solar Core, Radiative Zone, Convection Zone, Photosphere, Chromosphere, Transition Zone, and Corona.It explains that the Sun's outermost layer is hotter than the layers immediately below that. This is a major unsolved puzzle in heliophysics.
At the heart of our solar system is the Sun. Even though the temperature of these layers is known, heliophysicists are still researching why the Sun’s corona, or atmosphere, is hotter than the layers immediately below it. Credits: NASA