Abstract:
The equivalent widths of the g and K lines are measured at the pole and at the equator of the Sun during a period of minimum solar activity. The difference of temperature between pole and equator is evaluated by Woolley's method of the calcium ionization temperature. The pole is found to be hotter than the equator by 96° ± 18° or 86° ± 16°, depending upon the choice of the values of the continuous absorption coefficients. This result lends support to Bjerknes's thermohydrodynamical theory of sunspots. Using Bjerknes's theory, the depth of the sunspot umbral column is calculated from the observed difference of temperature between pole and equator and is found to be 125 km or 140 km.
