Johann Christoph Müller’s Sunspot Observations in 1719 – 1720: Snapshots of the Immediate Aftermath of the Maunder Minimum

• Published in: Solar physics 2021-10, Vol.296 (10), Article 154
• Main Authors: Hayakawa, Hisashi, Iju, Tomoya, Kuroyanagi, Chiaki, Carrasco, Víctor M. S., Besser, Bruno P., Uneme, Shoma, Imada, Shinsuke
• Format: Article
• Language: English
• Subjects: Amplitudes; Astrophysics and Astroparticles; Atmospheric Sciences; Extreme values; Hemispheres; Physics; Physics and Astronomy; Solar activity; Solar cycle; Solar minimum; Solar physics; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; Sunspot cycle; Sunspot groups; Sunspot numbers; Sunspots
• ISSN: 0038-0938; 1573-093X
• DOI: 10.1007/s11207-021-01880-8

The Maunder Minimum (1645 – 1715) was unique in terms of solar-cycle amplitudes and sunspot-position distributions registered in the last four centuries; however, little is known for its recovery and transition to the regular solar cycles until 1749 and the existing reconstructions vary from one to another here. This article presents a snapshot of Solar Cycle −3 including sunspot observations by Johann Christoph Müller (hereafter, JCM) in 1719 – 1720. We identified his sunspot drawings in the manuscript department of the National Library of Russia in St. Petersburg and compiled his biographical profile and observational expertise. Subsequently, we analysed his sunspot drawings and derived the group number and positions of the observed sunspots. The results and comparative analyses with contemporary observations revealed that JCM reported up to five sunspot groups, corresponding well with Sebastian Alischer’s records but contrasting with Johann Rost’s records in the existing databases. These comparisons indicated that Rost’s extremely large values recorded in 1719 – 1720 probably represented individual sunspot numbers instead of sunspot group numbers, unlike the understanding in the existing databases. Accordingly, JCM’s group number forms a robust reference for representing the solar activity in 1719 – 1720 and exhibits relatively moderate solar cycle amplitude in the immediate aftermath of the Maunder Minimum. Moreover, JCM’s sunspot drawings provide significantly detailed information on sunspot positions. Our analyses could locate the reported sunspot groups in both solar hemispheres, unlike those in the Maunder Minimum, which support the suggested transition between Solar Cycles −4 and −3.