Extension of the Solar Corona into Interplanetary Space

vational facts, and then in another column compare them with the results of the theoretical program we have been carrying out at Chicago over the past few years. The purpose of this comparison will be to suggest experiments, some of which are already in progress, and which will perhaps resolve a few of the difficulties in our present knowledge of the dynamics of the interplanetary medium. I shall start with the sun, since we believe, as Gold and others have pointed out, that it is the source of energy for all phenomena observed in the earth, in particular magnetic storms and auroras, and the source of energy for all the churning that apparently occurs in interplanetary space. Let me list a few basic facts about the sun that seem most pertinent to the problem. On the one hand, there is the solar corona, whose density at a height of 3 X 10 • km may be 3 X 107 atoms/cm 8. The corona is rather hot; active regions in the corona have temperatures, as determined by the Doppler widths of emission lines, of the order of 2 to 4 million degrees Kelvin. It is hardly necessary to point out that at these temperatures the gas will be completely ionized. The temperature observations which I quote here are determined only near the sun where the solar corona is sufficiently dense that its emission is visible. Very roughly the temperatures have been determined out to 3 solar radii.