The sun’s solar cycles were once around three years shorter than they’re today, a brand new evaluation of centuries-old Korean chronicles reveals. This previously unknown anomaly occurred during a mysterious solar epoch often called the “Maunder Minimum,” greater than 300 years ago.
The sun is consistently in a state of flux. Our home star cycles through periods of increased activity, often called solar maximum, when solar storms turn into more frequent and powerful, in addition to spells of reduced activity, often called solar minimum, when solar storms almost completely disappear.
It currently takes about 11 years for the sun to finish a solar cycle, from minimum to maximum and back again. Scientists can track the sun’s progress through a solar cycle by counting the variety of sunspots on the star’s surface, which appear more incessantly within the lead-up to and through solar maximum.
But just because the sun fluctuates inside individual cycles, historical sunspot records show that over longer periods, spanning many years or centuries, the general output of solar cycles also can rise and fall.
The Maunder Minimum, sometimes known as the Grand Solar Minimum, was a period of greatly reduced solar activity between 1645 and 1715 when sunspots “effectively disappeared,” Scott McIntosh, a solar physicist on the National Center for Atmospheric Research in Colorado who was not involved within the recent research, told Live Science in an email.
Related: The sun as you have never seen it: European probe snaps closest-ever photo of our star
During this time, the sun’s output was so low that average global temperatures also dropped, in what scientists have dubbed a “mini ice age,” in keeping with NASA — though it was also likely linked to high levels of volcanic eruptions on the time.
Sunspot records paint a general picture of the Maunder Minimum, which is called after the English astronomer Edward Walter Maunder. But there continues to be much concerning the period that scientists do not know.
In the brand new study, published Oct. 3 within the journal AGU Advances, researchers analyzed historic auroral records from Korea and located that solar cycles in the course of the Maunder Minimum were only eight years long on average — three years shorter than modern cycles.
The aurora records were a part of three separate books, or chronicles, written on behalf of Korean kings that contained detailed day by day reports of royal business, state affairs, weather and astronomical phenomena that occurred inside the Korean peninsula between 918 and 1910, in keeping with the 2021 study that first described them.
The astronomical sections of the chronicles incessantly speak of “red vapors” or “vapors like firelight.” The researchers imagine these descriptions seek advice from the West Pacific Anomaly (WPA) — an area above Korea that produces regular red auroras despite being removed from the magnetic poles. Like other auroras, the WPA occurs when solar radiation collides with Earth’s magnetic shield. But unlike other auroras on the time, these lightshows continued despite a decrease in solar activity since the Earth’s magnetic field is thinner on this region, which makes them a terrific proxy for solar cycle progression, the researchers wrote.
The dates when these auroras occurred show that solar radiation from the sun followed an eight-year cycle.
Scientists do not know what causes long-term solar cycle trends just like the Maunder Minimum, McIntosh said. There are “many things” that might influence solar activity over such long periods, he added. It’s also unclear why the solar cycles shortened during that point. But the brand new findings could provide “pivotal clues” in understanding this mysterious epoch in greater detail, researchers wrote within the paper.
Over the previous couple of solar cycles, solar activity has decreased barely, and there have been some slight fluctuations in cycle length. This led some experts to predict that we were entering a brand new epoch of reduced solar activity.
Nonetheless, the progression of the present solar cycle, which has been very energetic and is fast approaching solar maximum, suggests this will not be the case.