The Sun does not ease gently into dormancy. Instead its most violent outbursts of space weather stop abruptly at a distinct moment each cycle, and that moment holds the key to knowing how strong the following cycle will become.
Scientists have identified a previously unrecognised switch-off stage late in the solar cycle. The number of sunspots present when this stage arrives correlates closely with the peak sunspot count of the next cycle. The finding, presented at the Royal Astronomical Society's National Astronomy Meeting 2026 in Birmingham, makes it possible to forecast the strength of an upcoming cycle six to seven years before its maximum.
The switch-off occurs when more than 90 percent of active-region areas have migrated to within 15 degrees of the solar equator. At that latitude threshold the most extreme events cease. Professor Sandra Chapman of the University of Warwick captured the surprise:
The Sun does not gently go to sleep and then gently wake up again. Instead we have discovered that the most extreme space weather switches off quite suddenly at a specific point in every solar cycle.
An early application of the method suggests Solar Cycle 26 will reach a moderate peak of around 100 to 120 sunspots. The switch-off for the present Solar Cycle 25 is expected in roughly two years.
Practical value for infrastructure
Improved long-range forecasts give operators of satellites, electricity networks and communication systems more time to prepare. Space weather can induce geomagnetic storms that overload transformers, disrupt satellite orbits and black out radio links. Earlier notice translates into steadier power supplies and more resilient digital infrastructure at a time when societies depend on both.
The technique rests on careful counts of sunspots and the latitude migration of active regions. It does not eliminate the variability inherent in solar behaviour, yet it extends the reliable prediction window far beyond what earlier methods allowed. Traditional approaches have usually offered confidence only near solar minimum or maximum, leaving a gap of several years during which planners operated with limited foresight.