Anita Chandran interviews Dr Ryan Campbell
What do scientists mean by the Sun’s outer atmosphere?
It’s easiest to understand from the inside out. The photosphere is the Sun’s visible surface. It corresponds to a point in the Sun’s atmosphere where visible light or ‘visible photons’ from the Sun’s core can escape. Photons are emitted from atoms in the Sun’s core and then re-absorbed by other atoms. This happensof these trapped photons will escape from the Sun at the photosphere. As you get higher above the photosphere, first through the chromosphere and then to the corona, you expect things to get less hot and less dense. But something weird happens as you reach the corona. Instead of the temperature decreasing, it shoots way up. Nobody really understands why. This is a big unresolved question called the Coronal Heating Problem.