Transcript: Above the solar chromosphere is the corona, a diffuse outer layer of gas at the amazing temperature of two million degrees Kelvin. Both the chromosphere and the corona have higher temperatures than the photosphere. How can this be? One way for gas to become hot is pressure. Higher pressure and density will lead to higher temperature. This is what happens in the interior of the Sun, but the corona is a diffuse outer layer far from the Sun’s energy source. How can it be so hot? Think for example of a fluorescent tube. In this case a very diffuse gas in the tube is cool to the touch, yet it must have a thermal temperature of thousands of degrees Kelvin because it emits visible light. The reason is that it is given high energy by electrical fields that are pumped into it from electricity running through the tube. In the case of the solar corona the energy source is magnetic energy from the Sun’s surface and its magnetic field plus convection to carry the energy outward. The physics of the energy source in the solar corona is complex, but it’s clear that magnetic fields fuel the very high temperature of the solar corona.