What is the solar cycle?
The Sun is not a constant, steady star. Its magnetic field builds up, tangles, and then resets in a cycle that averages about 11 years. At one end of the cycle — solar maximum — the Sun's magnetic field is highly active: it's riddled with sunspots (dark, magnetically complex regions), prone to solar flares (explosive bursts of radiation), and produces frequent coronal mass ejections (CMEs) that blast billions of tonnes of plasma into space. At the other end — solar minimum — sunspot numbers drop to near zero, flares become rare, and the solar wind is relatively quiet and steady.
We measure solar activity primarily by counting sunspots. The international sunspot number (published monthly by the World Data Center for the Sunspot Index in Belgium) is the longest continuous record in astronomy — it goes back to Galileo's observations in 1610. The modern solar cycle series is numbered sequentially; Solar Cycle 1 began around 1755. Each cycle averages 11 years but varies between about 9 and 14 years.
The cycle is driven by the Sun's differential rotation (the equatorial regions rotate faster than the polar regions), which gradually winds and amplifies the Sun's magnetic field lines until they become so tangled that they erupt in flares and CMEs. After solar maximum, the magnetic field resets in a global polarity reversal — the north and south magnetic poles of the Sun switch. This happens at every solar maximum and is why the full magnetic cycle is actually 22 years (two 11-year sunspot cycles).
How solar maximum affects aurora
More solar activity means more aurora, through a direct causal chain:
- More sunspots → more active regions on the Sun's surface
- More active regions → more solar flares and coronal mass ejections
- More CMEs → more high-speed solar wind hitting Earth's magnetosphere
- More energetic solar wind → more geomagnetic storms
- More geomagnetic storms → more aurora, stronger aurora, aurora visible at lower latitudes
During solar maximum, the frequency of strong geomagnetic storms (Kp 5+) roughly doubles compared to solar minimum. Extreme events (Kp 7+) that might occur once every 18 months during minimum can happen multiple times per year during maximum. The auroral oval expands significantly during these storms, extending aurora visibility from Northern Norway (always good) to Southern Norway (occasional) to central Europe and the United States (rare but documented events).
Importantly, aurora doesn't disappear at solar minimum — Northern Norway remains under the auroral oval year-round, and even during the quietest years coronal holes continue to produce recurring high-speed solar wind streams that generate Kp 3–5 events. But the frequency, intensity, and geographic reach of aurora are all substantially reduced.
Solar Cycle 25: stronger than predicted
Solar Cycle 25 officially began in December 2019 (the previous solar minimum). The official forecast from the joint NOAA-NASA Solar Cycle 25 Prediction Panel, released in 2019, called for a modest cycle: a maximum smoothed sunspot number of about 115, comparable to the relatively weak Cycle 24, with the peak expected around July 2025.
Cycle 25 dramatically exceeded that forecast. By 2024, the smoothed sunspot number had already exceeded 150 and was still climbing. The cycle peaked earlier than predicted, and the activity levels reached were significantly above the official projections. The Science paper published by NOAA researchers in 2024 revised the peak prediction upward to SSN ~137 but even that has been exceeded.
What caused the mismatch? Solar cycle prediction is notoriously difficult. The physical mechanisms driving the cycle's amplitude are not fully understood — current models can predict the rough timing but not the strength of a cycle more than a year or two out. Cycle 24 was unusually weak, leading forecasters to project a weak Cycle 25 by analogy. The Sun had other plans.
The great storms of 2024–2025
The elevated Solar Cycle 25 produced a series of exceptional geomagnetic storms that brought the northern lights to latitudes they hadn't reached in decades:
May 10–12, 2024 — The Gannon Storm (Kp 9): The strongest geomagnetic storm since the Halloween Storms of 2003. Driven by a series of X-class flares and multiple CMEs, it produced Kp 9 (the maximum) for several hours. Aurora was visible across the continental United States (all 48 states), most of Europe, and as far south as Mexico, Cuba, and Hawaii. In Norway, the display was overwhelming — aurora visible in the daytime hours from Svalbard, covering the entire sky in vivid greens and reds from Tromsø. The Gannon Storm generated more aurora photographs and social media coverage than any event in recorded history.
October 2024 Halloween Storm (Kp 8–9): Another extreme event timed near the anniversary of the 2003 Halloween Storms. Multiple X-class flares and a fast CME arrived at Earth within 24 hours. Aurora visible from southern France, Spain, the northern United States, and southern Australia. The Tromsø display included rare all-red aurora and rapid substorm cycling that lasted 8+ hours.
Several Kp 6–8 events throughout 2024–2025: In addition to the extreme events, the frequency of moderate-to-strong storms was elevated across the entire year. During 2024, there were approximately 15 nights with Kp ≥ 6 — more than in any year of Cycle 24. Aurora was visible from Oslo, Bergen, and Stockholm on multiple occasions, making the northern lights accessible to millions of Scandinavians who normally never see them.
What solar minimum looks like for aurora chasers
Solar minimum doesn't mean no aurora — it means reduced aurora. During Cycle 24's minimum (around 2019–2020), the most active months still produced Kp 4–5 events visible from Northern Norway, and the auroral oval was still present above Tromsø on any clear, dark night. The difference is statistical:
- Kp 5+ events occur about 50–60 days per year during solar maximum vs 20–30 days during minimum
- Kp 7+ events: 5–10 per year at maximum vs 1–3 per year at minimum
- Kp 9 events: can occur multiple times in a maximum year; may not occur at all during a minimum year
For visitors to Tromsø or Lofoten, a solar minimum year is still a good aurora year. The auroral oval is always overhead, and Kp 2–3 events (which produce excellent local displays) happen regularly year-round. What you lose is the chance of seeing the aurora from your hometown in central Europe, and the probability of witnessing a truly extraordinary multi-Kp 8–9 event drops sharply.
How to plan around the solar cycle
For most aurora travellers, the solar cycle is a background context factor, not a trip planner. Here's how to think about it:
- If you're visiting Northern Norway (Tromsø, Lofoten, Svalbard): The solar cycle matters less because you're inside the auroral oval regardless. Any clear dark night gives you aurora. The cycle affects how spectacular that aurora is — a Cycle 25 maximum night in January might produce a Kp 6 display; a cycle minimum January might give you Kp 2–3. Both are good. The key variable is still cloud cover, not solar cycle.
- If you want aurora from lower latitudes (Oslo, Bergen, Scotland, Scandinavia below 65°N): The solar cycle matters much more. During maximum years like 2024–2026, Kp 5–7 events that reach these latitudes occur dozens of times per year. During minimum years, you might wait an entire winter for a single visible event.
- Bucket list once-in-a-decade viewing: 2024–2026 is the window. The current cycle peak is the best aurora opportunity many Europeans will see in their lifetime, given that Cycle 26 is not expected to peak until 2034–2036.
The next solar maximum
Solar Cycle 25 activity will decline gradually from its 2024–2025 peak. Activity remains elevated for roughly 2–3 years around the peak, so 2026 should still be an active year for aurora, particularly in its first half. By 2027–2028, activity will be noticeably declining. Solar minimum for Cycle 25 is currently projected around 2030–2031.
Solar Cycle 26 will begin around 2030 and reach its maximum around 2034–2036. Whether Cycle 26 will be stronger or weaker than Cycle 25 is not yet possible to predict reliably — solar cycle forecasting only becomes reasonably accurate about 1–2 years before the cycle's maximum. The official NOAA-NASA forecast panel will release a Cycle 26 prediction around 2029.
Does the solar cycle affect aurora season timing?
No — aurora season in Norway is determined by Earth's tilt and rotation, not solar activity. The sun never gets below the horizon at Tromsø from mid-May through late July regardless of solar cycle phase. You cannot see aurora in Norwegian summer because of the midnight sun, period. The solar cycle changes the probability and intensity of aurora during the dark months, but it cannot extend the season.
One nuance: during very active storm periods (Kp 8–9), aurora has been photographed against twilight sky during the marginal months of April and early August in Norway, when the sun is below the astronomical horizon but not yet fully dark. These are exceptional cases during extreme events, not regular aurora season extension.