The butterfly diagram in the 18th century

Abstract

Digitized images of the drawings by J.C. Staudacher were used to determine sunspot positions for the period of 1749-1796. From the entire set of drawings, 6285 sunspot positions were obtained for a total of 999 days. Various methods have been applied to find the orientation of the solar disk which is not given for the vast majority of the drawings by Staudacher. Heliographic latitudes and longitudes in the Carrington rotation frame were determined. The resulting butterfly diagram shows a highly populated equator during the first two cycles (Cycles 0 and 1 in the usual counting since 1749). An intermediate period is Cycle 2, whereas Cycles 3 and 4 show a typical butterfly shape. A tentative explanation may be the transient dominance of a quadrupolar magnetic field during the first two cycles.