The 8-Year Solar Cycle During the Maunder Minimum

The presence of grand minima, characterized by significantly reduced solar and stellar activity, brings a challenge to the understanding of solar and stellar dynamo. The Maunder Minimum (1645–1715 AD) is a representative grand solar minimum. The cyclic variation of solar activity, especially the cycle length during this period, is critical to understand the solar dynamo but remains unknown. By analyzing the variations in solar activity-related equatorial auroras recorded in Korean historical books in the vicinity of a low-intensity paleo-West Pacific geomagnetic anomaly, we find clear evidence of an 8-year solar cycle rather than the normal 11-year cycle during the Maunder Minimum. This result provides a key constraint on solar dynamo models and the generation mechanism of grand solar minima.