???? Old texts reveal strange anomalies in the Sun cycle

2023-10-24 11:00:04

The Sun’s cycles were once regarding three years shorter than they are today, a new analysis of ancient Korean texts reveals. This anomaly, little known until now, occurred during a period called the “Maunder Minimum”, more than 300 years ago.
Comparison of the Sun during solar maximum (left) and solar minimum (right).
Crédit: NASA/Solar Dynamics Observatory

The Sun is constantly evolving. It alternates between periods of increased activity, called solar maximum, and periods of reduced activity, known as solar minimum. Today, a solar cycle lasts approximately 11 years, from minimum to maximum and vice versa. Scientists follow these cycles by counting the number of sunspots on the surface. …) of the Sun.

Over the centuries, these cycles have fluctuated. The Maunder Minimum, or Grand Solar Minimum, was a period of extremely low solar activity between 1645 and 1715. According to Scott McIntosh, a solar physicist at the National Center for Atmospheric Research in Colorado, sunspots then “almost disappeared.”

Annotated section of Korean historical texts mentioning auroras during the Maunder Minimum.
Credit: Yan et al. 2023

This decline in activity has also led to global climate cooling, often referred to as a “mini ice age.” A new study has found that during the Maunder Minimum, solar cycles were on average only eight years long, three years shorter than now. .

The researchers used records in books written for Korean kings between 918 and 1910. These records often mentioned “red vapors,” probably aurora, despite declining solar activity. These data suggest that solar activity then followed an eight-year cycle.

This graph shows how solar activity decreased during the Maunder Minimum.
Crédit: NASA/University of Colorado’/LASP Interactive Solar Irradiance Datacenter

The cause of these long-term trends remains unknown. Nevertheless, these new discoveries might provide crucial clues to understanding this epoch of the Sun.
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