Abstract:
BothEmden's/sup1 old hydrodynamic solar theory and the more modern thermo-hydrodynamical solar theory due to Bjerknes/sup2 lead to a higher temperature at the poles than at the equator of the sun. Bjerknes's theory is, however, more definite as regards the order of temperature difference to be expected. Bjerknes regards the sun as a baroclinic cosmic vortex in which there is a stratified circulation directed from the poles to the equator in the upper photospheric layer and a reverse circulation in the layer immediately below. According to him, sunspots, which he considers also to be vortices, originate in the sub-photospheric stratum; and the depth of a sunspot vortex is connected with the actual difference of temperature between the pole and the equator of the sun. This difference of temperature thus acquires a special importance in solar physics, and therefore an observational determination of this quantity is greatly to be desired. To our knowledge, no measurement of this quantity is so far available. The reason for this lacuna is perhaps to be found in the difficulty of measuring the temperature of the sun with the required degree of accuracy; for the usual methods of measuring the effective temperature of the sun cannot be trusted to give an accuracy greater than +/- 400° or 500°. But the temperature difference between the poles and the equator might be of the order of 100° or even less, so that some procedure capable of a higher precision is evidently required.
