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The Sun's structure consists of 6 layers starting with core and extending out through the Radiative Zone, Convective Zone, Photoshere, Chromosphere, and the Corona. The core makes up ~12% of the suns radius and 10% of the total mass. Unlike the Earths iron core the Sun's core is a Nuclear Fusion engine made up of densely packed plasma producing temperatures in excess of 15,700,000 K (~28,000,000 F) and held together by gravitational forces. The density of the core is estimated to be 140 times that of water and is surrounded by the Radiative Zone.The Radiative layer constitutes ~73% the radius and is cooler (~5,000,000 K or ~9,000,000). This has an insulating effect on the core while allowing heat transfer. Heat is transferred to the outer layers by gamma photons, resulting from core fusion, being absorbed and re-emitted repeatedly transferring heat from nuclei to nuclei. These radiation particles bounce around in the radiation zone for many hundreds of thousands to millions of years before reaching the Convection Zone. |
The Convection layer makes up the final ~15% of the Sun's radius. The temperature gradient is extremely steep dropping the temperature from 2,000,000 K (~3,600,000 F) to 6,000 K (~10,000 F). Plasma particles closer to the radiative zone are hotter and rise to the surface while cooler particles fall back inward resulting in convection currents. By themselves the particles are still too hot and dense to be expelled from the sun due to gravitational forces. The thermal columns of convection action create granulations on the surface of the sun and create the unique look of the Photosphere.
The Photosphere is the visible surface of the sun with a temperature around 6,000 K and produces most of the visible white light. The photoshpere has darker and lighter regions that pothole the suns surface. These regions are result for the hotter (light regions) plasma rising up from the convection currents and cooler (darker regions) plasma falling back towards the sun's core. This constantly changing convection pattern is known as the solar granulation pattern and produces strong magnetic fields. Above the photoshpere is the Chromosphere.
The Chromosphere is the beginning of the suns atmosphere and is hotter then the photosphere with temperatures rising up to 20,000 K (~35,500 F). Its name is the result of the reddish appearance that it gives off and requires special Hydrogen-Alpha filters to observe except during a full solar eclipse. For many years it was unclear why the chromosphere was hotter then the photosphere. With the help of the Solar and Heliospheric Observatory (SOHO) and the Transition Region And Coronal Explorer (TRACE), solar physicists have identified patches of magnetic fields covering the surface of the sun and it is believed that these magnetic fields play a major role in the higher temperatures. There are still a lot of unknowns and disagreements among physicist about this increase in temperature which extends beyond the chromosphere and into the Corona.
The Corona is millions of time less bright then the photosphere but reaches temperatures of 2,000,000 F. Like the chromosphere it can only be observed with the naked eye during a total eclipse of the sun. Special instruments called Coronagraph are required to view the corona any other time. A coronagraph artificially blocks the disk of the sun much like an eclipse making observation possible. The corona is divided into two regions. The inner corona extends for millions of kilometers into space and is what we can see with special instrumentation or a total eclipse of the sun. The outer region is known as Solar Winds and it extends beyond the Earth. The solar winds change based on the suns activity and have an impact on our planet.