The great sunspot of January 1938

A large group of sunspots in latitude +17° came into view at the east edge of the Sun on January 12, 1938. It was very complicated in structure (Fig. 1), consisting of a very irregular penumbra within which were several umbrae as well as areas of approximately photospheric brightness. The regions of opposite magnetic polarities were not separated into distinct spots as they are in a typical bipolar group. The regions of positive polarity were, however, in the north‐preceding part of the group and those of negative magnetic polarity in the south‐following part.Three very great magnetic storms occurred between January 12 and 26. The first, January 16–18, began when the center of the group was 21° east of the central meridian; the second, January 21–22, began when the group was 42° west of the central meridian; and the third, January 25–26, began one day after the group had passed around the west limb of the Sun.