Aurora records reveal shortened solar cycle during Maunder minimum
"Sunspots change in number depending on how much magnetic activity the solar dynamo generates. But there's not total chaos: These changes occur in a cycle, which lasts about 11 years on average. The sun also experiences extended periods of low activity that can last for decades, called grand minima. The Maunder minimum, which occurred between 1645 and 1715, is often viewed as an archetypal example of the sun's behavior during these abnormal periods.
Historical data on the sun's behavior during the Maunder minimum, including records of sunspot activity and radionuclide deposition, are sparse and do not always align. To bolster knowledge of the solar dynamo during the Maunder minimum, Limei Yan and colleagues turned to a new source of data: observations of equatorial aurorae in Korean historical texts.
Korean historians kept meticulous records of events during the Joseon dynasty, which spanned the 14th to 19th centuries. These records include observations of the night sky, such as aurorae, which could be seen regularly during much of the Joseon dynasty because of a geomagnetic anomaly in the west Pacific. Aurorae are correlated with the solar cycle and happen more frequently during periods of high activity."
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