How the Sun goes to ‘sleep’ can tell us a lot about future space weather, scientists reveal

For decades, scientists have tried to guess what the Sun will do next, and mostly failed. Why? Because the star’s magnetic tantrums appear in roughly 11-year cycles, and no two cycles behave in the same way. Some are fierce, while others are mild. And sometimes they spring surprises that catch scientists off guard.Now researchers at the University of Warwick have developed a new method to predict the strength of the Sun’s next activity level. The researchers found a precise point where the Sun’s most violent space weather abruptly shuts off, like a switch flipping. That ‘switch-off’ point holds the key to forecasting the strength of the next solar cycle up to seven years in advance. The findings are being presented at the Royal Astronomical Society’s National Astronomy Meeting in Birmingham.

What the Sun’s sleep cycle reveals about its next solar cycle

Using the new approach, researchers have made an early prediction for the strength of Solar Cycle 26. The upcoming cycle may be moderate, with roughly 100–120 sunspots at peak, which is similar to or slightly weaker than Cycle 25. However, this is a preliminary estimate. For more precision, researchers will have to wait until the current Solar Cycle 25 reaches its switch-off point, which is expected in about two years, when observations can replace projections.‘The Sun doesn’t gently go to sleep and then gently wake up again. Instead, we’ve discovered that the most extreme space weather switches off quite suddenly at a specific point in every solar cycle. By identifying that point, we’ve found a new way to predict how active the next solar cycle is likely to be,’ Sandra Chapman, Professor of Physics and Director of the Centre for Fusion, Space and Astrophysics at the University of Warwick, said in a statement.She added that the team would be able to refine the predictions in about two years. That is when Solar Cycle 25 reaches the newly identified ‘switch-off’ point.

Inside the Sun’s cycle

Our Sun follows an approximately 11-year cycle. During this period, its magnetic field reverses polarity, and the number of sunspots rises and falls. These sunspots are regions of intense magnetic activity, which can produce powerful solar flares and coronal mass ejections. All these contribute to space weather, which can also affect the Earth. It can affect satellites, communications, navigation systems and power grids on Earth. Though astronomers have studied sunspots for centuries, they could not predict the Sun’s next cycle, as no two solar cycles are the same. There are differences in both length and intensity.That is where the new method is crucial. It is built on Chapman’s earlier work involving what they called the ‘sunclock’, which maps the Sun’s irregular cycles onto a standard clock. The new method revealed that the Sun’s most extreme weather does not fade gradually. It ceases abruptly at a distinct moment in each solar cycle. The researchers found that the number of sunspots present at this switch-off point, when extreme space weather suddenly terminates, is closely linked with the peak number of sunspots in the following cycle. By counting sunspots at this moment, researchers can predict the strength of the next solar cycle six to seven years before it reaches its maximum, far earlier than traditional methods allow.

Pic courtesy: NASA/SDO

The new method also identifies a specific stage in the solar cycle when the magnetic field that drives the next cycle should become established. This will help researchers understand the solar dynamo, which is the process that generates the Sun’s magnetic field.‘We’re about two years away from the switch-off point for the current Solar Cycle 25. At the moment, we have to estimate where that point will be, but once we reach it we can use observations alone to make a much more precise prediction for Solar Cycle 26. That will still give us around seven years’ warning of how strong the cycle is likely to be,’ Professor Chapman said.This method successfully predicted that Solar Cycle 25 would be stronger than expected, and that it could result in spectacular auroras in recent years. The UK experienced a series of historic solar storms in 2024 as the cycle approached its maximum. Driven by a cluster of massive sunspots, these events produced the most powerful geomagnetic disturbances to strike Earth in more than two decades. What followed was a display of vivid Northern Lights across the UK, as far south as Devon and Cornwall, a rare sight for southern England.