The Maunder Minimum (1645–1715; hereafter MM) is generally considered as the only grand minimum in the chronological coverage of telescopic sunspot observations. Characterized by scarce sunspot occurrences and their asymmetric concentrations in the southern solar hemisphere, the MM has frequently been associated with a special state of solar dynamo activity. As such, it is important to analyze contemporary observational records and improve our understanding of this peculiar interval, whereas the original records are frequently preserved in historical archives and can be difficult to access. In this study, we consult historical archives in the National Library of Russia, St. Petersburg, and analyze a series of sunspot observations conducted at the Eimmart Observatory from 1681 to 1709, which is the second-richest sunspot data set produced during the MM, following La Hire's series, among existing data sets. We have further extended our analyses to neighboring observations to extend our investigations up to 1718. We first analyze source documents and descriptions of observational instruments. Our analyses have significantly revised the existing data set, removed contaminations, and updated and labeled them as Eimmart Observatory (78 days), Altdorf Observatory (4 days), Hoffmann (22 days), and Wideburg (25 days). The revisions have updated the temporal coverage of the contemporary sunspot observations from 73.4% to 66.9% from 1677 to 1709. We have also derived the positions of the observed sunspot groups in comparison with contemporary observations. Our results indicate hemispheric asymmetry in the MM and recovery of sunspot groups in both hemispheres after 1716, supporting the common paradigm of the MM.

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.

The Maunder Minimum (MM) was a period of prolonged solar activity minimum between 1645 and 1715. Several works have identified a significant number of problematic spotless days in the MM included in existing data bases. We have found a list of exact spotless (in the second half of 1709) and spot days (January and August 1709) provided by Johann Heinrich Müller. We computed the most probable value and upper/lower limits of the active day fraction (ADF) from Müller's data using the hypergeometrical probability distribution. Our sample is not strictly random because Müller recorded observations in consecutive days when he observed sunspots. Therefore, our result represents an upper threshold of solar activity for 1709. We compared this result with annual values of the ADF calculated for the Dalton Minimum and the most recent solar cycles. We concluded that, although 1709 is one of the most active years in the MM, it was less active than most years both in the Dalton Minimum and in the most recent solar cycles. Therefore, the solar activity level estimated in this work for 1709 represents robust evidence of low solar activity levels in the MM.