How does the radius of the Sun compare to that of Earth?
• It is more than 100 times bigger. What are the approximate temperatures of the chromosphere and Corona, in degrees centigrade? • About 50,000° and 1,000,000°. Why is that so puzzling? • Because the only credible source of the heat is the Sun itself. However, heat always flows from a hot temperature to a lower one–never the other way around. The photosphere below these layers is cooler: how then can it heat the chromosphere and corona? How can we be sure that the corona is so hot? • The light from the corona is characteristic of atoms which have lost quite a few electrons (more about that, in a later lesson). At the density of the corona, this requires collisions between fast atoms, and the speed of the atoms of a gas is directly related to its temperatures. So, what can be the explanation of the heat of the corona? • The energy must arrive at the corona in a form different from heat–perhaps as sound-like waves, or as a population of fast ions produced by such waves. Any older expla
