Underneath every day-to-day Kp number and every individual CME sits a much slower rhythm: the roughly 11-year solar cycle. It doesn’t determine whether you’ll see the aurora on a specific night, but it strongly shapes how often the opportunity for a strong display comes around at all, especially for storm-only, mid-latitude destinations.
What actually drives the 11-year rhythm
The leading physical explanation is known as the Babcock-Leighton dynamo model. The Sun doesn’t rotate as a solid body — its equator completes a rotation in a little over 24 days, while regions near its poles take closer to 35 days, a phenomenon called differential rotation. Over time, this uneven rotation stretches and winds the Sun’s large-scale magnetic field lines like a rubber band being twisted around an unevenly spinning axle. Where that winding becomes concentrated enough, buoyant loops of magnetic field rise up through the surface, appearing as sunspot pairs — regions of intense magnetic field that appear dark because they’re cooler than the surrounding surface, suppressing the convective heat transport that would otherwise keep that patch of surface at normal brightness.
As a cycle progresses, this process gradually reorganises the Sun’s global field, and roughly every 11 years the whole system reaches a tipping point: the Sun’s global magnetic polarity flips (a pattern known as Hale’s polarity law, where sunspot pairs in one hemisphere consistently show one magnetic orientation during one cycle and the reverse orientation during the next), and the field resets to a simpler, less wound-up configuration before the winding process begins building toward the next peak. A useful, if partial, visual for this rhythm is the “butterfly diagram” — a chart of sunspot latitude against time, which shows spots emerging at mid-latitudes early in a cycle and gradually migrating toward the equator as the cycle matures, forming a distinctive wing-shaped pattern when successive cycles are plotted side by side.
What the solar cycle actually is, in observable terms
The most visible marker of where the Sun sits in this cycle is sunspot count, tracked using the International Sunspot Number — a standardised count combining both the number of individual spots and the number of distinct spot groups, scaled against a continuous historical baseline stretching back to the 1700s so that counts from different eras and observatories remain comparable. Near solar minimum, the Sun’s face can go days or weeks with no visible sunspots at all; near solar maximum, dozens of active sunspot regions can be present at once, with monthly smoothed sunspot numbers commonly running well over 100 during a strong cycle’s peak, compared with numbers close to zero at minimum.
Sunspots matter for aurora chasers because they mark regions of concentrated, twisted magnetic field — exactly the kind of region that produces solar flares and, more importantly for aurora, coronal mass ejections (see what is a CME). More sunspots generally means more frequent and more powerful CMEs, which means more frequent and more powerful geomagnetic storms.
Where Solar Cycle 25 stands
Solar Cycle 25 began around December 2019, following an unusually quiet Cycle 24, and its sunspot numbers came in noticeably higher than many early-cycle predictions expected — a genuine surprise to some forecasters, since a handful of statistical methods had projected a cycle even weaker than the quiet Cycle 24 that preceded it. Most solar physicists place its peak — solar maximum — in the 2024-2025 window, based on smoothed sunspot counts, though as with every solar cycle, the precise peak is only confidently identified some time after it has passed, once enough data has accumulated to smooth out short-term noise (a pattern sometimes called the Waldmeier effect, where cycles that rise faster to their peak also tend to reach a higher peak, giving forecasters an early, if imperfect, clue partway through the rising phase).
Some of the most widely reported recent aurora events, visible at unusually low latitudes — including displays photographed as far south as Melbourne, Berlin and much of the contiguous United States during the May 2024 storm — occurred during this cycle’s active years, a reminder that strong storms cluster around, but aren’t limited to, the exact peak month.
The declining phase isn’t a quiet phase
It’s a common misconception that aurora activity falls off sharply the moment solar maximum passes. In practice, the years after the peak — the declining phase — often remain quite active, for a specific structural reason: large, long-lived coronal holes tend to become more prominent as the cycle winds down, driving the kind of steady, recurring geomagnetic activity described in coronal holes and recurrent storms. Some of history’s most-cited strong storms have occurred one to three years past a cycle’s sunspot-number peak, so “the maximum has passed” is not the same as “the good years are over.” For storm-only cities such as London or New York, the declining phase can, in some cycles, produce a comparable or even better run of visible events than the peak itself, simply because recurrent coronal-hole activity adds to whatever CME activity is still occurring from lingering active regions.
The historical extremes: what a truly quiet Sun looks like
The 11-year rhythm has not always held with perfect regularity. The Maunder Minimum, spanning roughly 1645 to 1715, was an extended period during which sunspots were rare for decades at a stretch — a dramatic departure from the usual cycle, and one that coincided with (though isn’t conclusively proven to have caused) a colder period in parts of Europe sometimes referred to as the Little Ice Age. Whether an extended quiet period like this could recur is a genuinely open research question. Nothing in Solar Cycle 25’s behaviour suggests one is imminent, but the historical record is a useful reminder that the reliable-seeming 11-year rhythm is an average pattern, not an ironclad guarantee, over long enough timescales.
Looking ahead to Solar Cycle 26
Based on typical cycle lengths, Solar Cycle 26 is expected to begin sometime in the early-to-mid 2030s, following Cycle 25’s eventual minimum. Predicting a cycle’s strength this far in advance is genuinely difficult — solar cycle prediction has historically had a mixed track record, with methods based on the Sun’s polar magnetic fields near the preceding minimum (a technique with a notably better track record than older sunspot-count extrapolations for Cycle 25 itself) showing more promise, but still carrying real uncertainty. Meaningful forecasts for Cycle 26’s likely strength will firm up as it approaches and the preceding minimum’s characteristics become clearer, likely sometime in the early 2030s.
What this means for planning an aurora trip
For destinations already inside the auroral oval — the flagship tier-one towns covered on this site, like Tromsø — the solar cycle mostly affects how often and how dramatic the displays are, not whether they happen at all; even relatively quiet years still produce regular aurora at these latitudes. For storm-only, mid-latitude cities, the solar cycle matters much more directly: the handful of nights per cycle when the aurora becomes visible from London, Berlin, or the northern US cluster disproportionately around the active years — roughly the few years centred on and following solar maximum. If a mid-latitude aurora sighting is genuinely the goal, timing a trip (or at least paying closer attention) during those years meaningfully improves the odds, though it’s never a guarantee — see planning an aurora trip: how many nights do you need for how to think about the odds practically rather than just the calendar.
Frequently asked questions
When is solar maximum for Solar Cycle 25?
Solar physicists generally place the peak of Solar Cycle 25 around 2024-2025, based on sunspot counts, though solar maximum is only clearly identified in hindsight — the exact peak month is typically confirmed well after the fact.
Does solar activity drop off a cliff after solar maximum?
No — it declines gradually over several years, and the declining phase often features its own strong storms, particularly from large, persistent coronal holes. Some of the most memorable storms in recent solar cycles have actually occurred a year or more past the sunspot-number peak.
Will Solar Cycle 26 be stronger or weaker than Cycle 25?
This isn't reliably predictable this far out. Solar cycle strength forecasting has a mixed track record, and meaningful predictions for Cycle 26 (expected to begin around the early-to-mid 2030s) won't firm up until the cycle is already underway.
Does a strong solar cycle mean stronger aurora at flagship destinations too?
It mostly increases the frequency and intensity of storms, which matters most for storm-only, mid-latitude cities that need a big event to see anything at all. Flagship destinations already inside the auroral oval see displays in most solar cycle phases, just somewhat more often and more dramatically near maximum.
What actually causes the 11-year cycle in the first place?
The leading explanation is the Babcock-Leighton dynamo model: differential rotation (the Sun's equator rotates faster than its poles) stretches and winds up the Sun's magnetic field over time, building up the twisted, concentrated field regions that surface as sunspot pairs. Roughly every 11 years, this wound-up field reaches a point of reorganisation, the Sun's global magnetic polarity flips, and the cycle effectively restarts with the field in a simpler, less twisted state.
What is the "butterfly diagram," and why do solar physicists reference it?
It's a chart plotting sunspot latitude against time across a cycle, and it reliably shows sunspots first appearing at mid-latitudes early in a cycle, then drifting toward the equator as the cycle matures -- forming a wing-shaped, butterfly-like pattern when cycles are stacked one after another. It's one of the most distinctive, reliably repeating patterns in solar physics, and a genuinely useful visual for seeing where a cycle currently stands.
What was the Maunder Minimum, and could something like it happen again?
The Maunder Minimum (roughly 1645-1715) was an extended period of unusually low sunspot activity, coinciding with a colder period in parts of Europe sometimes called the Little Ice Age, though the causal link to climate is debated among historians and climatologists. Whether another such extended quiet period could recur is an open research question -- nothing in current solar cycle behaviour points to one being imminent, but the historical record shows the 11-year rhythm is not perfectly guaranteed to continue indefinitely at its usual strength.
How is the sunspot number actually counted?
The most commonly cited figure, the International Sunspot Number, uses a formula that counts both individual sunspots and the number of distinct sunspot groups they belong to, combined and scaled against a long historical baseline so that counts from different observatories and eras can be compared consistently -- it is a maintained, standardised measurement with a continuous record stretching back to the 1700s.