The butterfly diagram in the 18th century

TL;DR

This study digitized and analyzed 18th-century sunspot drawings to reconstruct the butterfly diagram, revealing early solar activity patterns and magnetic field configurations during 1749-1796.

Contribution

It provides the first detailed sunspot position dataset from the 18th century and interprets magnetic field evolution based on historical observations.

Findings

Early cycles show a highly populated equator.

Transition to typical butterfly shape occurs in later cycles.

Possible link between magnetic field configuration and sunspot distribution.

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.