The records from Aurora show a shortened solar cycle during the Maunder Minimum.

Source: AGU Advances

The amount of sunspots present is influenced by the magnetic activity of the solar dynamo. However, these changes follow a predictable cycle lasting approximately 11 years. The Sun can also go through prolonged periods of reduced activity, known as grand minima, which may last for several decades. The Maunder Minimum, observed from 1645 to 1715, is often seen as a typical illustration of the Sun’s behavior during these anomalous 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, Yan et al. turned to a new source of data: observations of equatorial aurorae in Korean historical texts.

During the Joseon dynasty, Korean historians carefully documented events, including observations of the night sky. Notably, they recorded the occurrence of aurorae, a natural phenomenon that appeared regularly due to a geomagnetic anomaly in the west Pacific. The frequency of aurorae is influenced by the solar cycle and is more common during times of heightened activity.

The scientists utilized a preexisting collection of Korean historical documents to examine 1,012 instances of auroras from 1620 to 1810. Through observing the frequency of auroras, they discovered a relatively brief solar cycle of 8 years during the Maunder Minimum.

Their research contributes to existing data about the Sun’s behavior and suggests that the solar cycle may have been shortened during the Maunder Minimum. This shift could suggest that the solar dynamo operates differently during periods of grand minima, although the reason for this is not yet understood. (Published in AGU Advances, https://doi.org/10.1029/2023AV000964, 2023)

—Nathaniel Scharping (@nathanielscharp), Science Writer

Reference: Scharping, N. (2023), Maunder Minimum Shows a Decreased Solar Cycle in Aurora Records, Eos, 104, https://doi.org/10.1029/2023EO230384. Published on October 10, 2023.

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