An Overview of Sunspot Observations in the Early Maunder Minimum: 1645-1659

Within four centuries of sunspot observations, the Maunder Minimum (MM) in 1645-1715 has been considered a unique grand minimum with weak solar cycles in group numbers of sunspots and hemispheric asymmetry in sunspot positions. However, the early part of the MM (1645-1659) is poorly understood in terms of its source records and has accommodated diverse reconstructions of the contemporaneous group number. This study identified their source records, classidied them in three different categories (datable observations, general descriptions, and misinterpreted records), and revised their data. On this basis, we estimated the yearly mean group number using the brightest star method, derived the active day fraction (ADF), reconstructed the sunspot number based on ADF, and compared them with proxy reconstructions from the tree-ring data sets. Our results revised the solar activity in the early MM downward in yearly mean group numbers using the brightest star method and upward in the active day fraction and sunspot number estimates. Our results are consistent with the proxy reconstruction for 1645-1654 and show more realistic values for 1657-1659 (against the unphysical negative sunspot number). These records have paid little attention to sunspot positions, except for Hevelius' report on a sunspot group in the northern solar hemisphere in 1652 April. Therefore, slight caveats are required to discuss if the sunspot positions are located purely in the southern solar hemisphere throughout the MM.