Solar & seasonal
The sunspot cycle
The sunspot cycle is the roughly 11-year rise and fall in the number of dark spots on the Sun's surface, the visible sign of the star's changing magnetic field. This is the Schwabe cycle, named for the amateur astronomer who first noticed the pattern in the 1840s. Its length is not fixed: individual cycles have run anywhere from about 9 to 14 years, and the modern average measured minimum to minimum is close to 10.7 years.
Unlike the tropical year or axial precession, this is not a clockwork orbital period you can compute from geometry. It is a data-driven cycle, read off the observed Sun and reconstructed from centuries of counts. Every value here is a measurement with real uncertainty, not an exact ephemeris quantity, and forecasts of the next minimum carry error bars for that reason.
On this page
We are in Solar Cycle 25, which began around December 2019 and passed its maximum in 2024 to 2025 according to the SILSO sunspot record. The next minimum is expected around 2030.
The count of sunspots rises and falls on a roughly 11-year rhythm, the Schwabe cycle; the Sun's magnetic polarity flips each cycle, so the full magnetic Hale cycle is about 22 years.
Where we are in the sunspot cycle right now
The current cycle is Solar Cycle 25, past its 2024 to 2025 maximum (SILSO) and heading toward a minimum around 2030. This is an observed, data-driven rhythm, so its timing is an estimate. The milestones below come from the SILSO record and forecasts.
The sunspot cycle is tracked from the SILSO sunspot-number record, not an ephemeris, so the figures here are observed data and estimates. See every cycle together on the cosmic clock.
The sunspot cycle at a glance
| Mean period | about 11 years (the Schwabe cycle) |
|---|---|
| Range of individual cycles | about 9 to 14 years |
| Modern average, minimum to minimum | about 10.7 years |
| Full magnetic cycle (Hale) | about 22 years |
| Type | observed, data-driven; not an orbital period |
| Current cycle (SILSO) | Solar Cycle 25, began around December 2019 |
| Cycle 25 maximum (SILSO) | reached 2024 to 2025 |
| Next minimum (SILSO estimate) | around 2030 |
| Measured from | the SILSO sunspot-number record |
Sources: SILSO, Royal Observatory of Belgium (World Data Center for the sunspot number).
The sunspot cycle in every unit
Because the sunspot cycle is measured rather than computed, its length is best expressed as a range and an average, alongside the longer magnetic cycle it belongs to.
| Mean period | about 11 years |
|---|---|
| Mean period in days | about 11 x 365.25 d = about 4,018 d |
| Modern average, min to min | about 10.7 years = about 3,908 d |
| Shortest to longest observed | about 9 to 14 years |
| Two Schwabe cycles | about 2 x 11 yr = the full magnetic Hale cycle, about 22 years |
| Solar Cycle 25 so far (SILSO) | began around December 2019, maximum 2024 to 2025 |
| Cycle 25 length to next minimum (SILSO estimate) | about 2019 to about 2030 = roughly 11 years |
Values are measurements from the SILSO sunspot-number record, not derived constants; the day figures are approximate and depend on which minima are chosen. Current-cycle timing is the SILSO estimate and carries real uncertainty.
What the sunspot cycle is and how it arises
Sunspots are regions where intense magnetic fields, thousands of times stronger than the surrounding surface, punch through the Sun's outer layers. The field chokes off the upward flow of hot gas from below, so a spot is cooler and darker than the surrounding photosphere. Their number tracks how tangled and active the Sun's overall magnetic field is at a given time.
The cycle arises from a dynamo deep inside the Sun. The Sun does not rotate as a solid body: its equator turns faster than its poles, and this differential rotation, working with churning convection, winds up and amplifies the magnetic field over years. As the field grows twisted, more spots appear, activity climbs to a maximum, and then the field reorganizes and decays toward minimum.
The magnetic polarity of the Sun flips from one 11-year cycle to the next. The north and south magnetic poles trade places, and the leading spots in each hemisphere reverse their magnetic sign. Only after two Schwabe cycles does the field return to its original polarity, which is why the full magnetic cycle, the Hale cycle, runs about 22 years.
The math
There is no formula for the sunspot cycle in the way there is for an orbit. You cannot plug in masses and distances and get 11 years out. Instead the period is measured from the SILSO sunspot-number record, the long homogeneous series of daily and monthly counts maintained at the Royal Observatory of Belgium. Cycle length is taken from one minimum to the next.
Over the modern record that spacing averages about 10.7 years, but it is not stable: individual cycles span roughly 9 to 14 years, and their peak amplitude varies just as much. Because it is an empirical average of a noisy, physically variable process, any single number for the period is a summary, not a constant, and forecasts of the coming minimum or maximum are stated with genuine uncertainty.
For where the Sun sits today in this rhythm, along with its position among the other astronomical cycles, see the interactive summary on the cycles hub.
Where the sunspot cycle stands
| Date | Milestone (observed or estimated) |
|---|---|
| December 2019 | Cycle 24 minimum; Cycle 25 begins |
| 2024 to 2025 | Cycle 25 maximum (SILSO) |
| around 2030 | Cycle 25 minimum (expected) |
| around 2035 | Cycle 26 maximum (expected) |
How the sunspot cycle relates to other cycles
The sunspot cycle sits apart from its siblings on this site precisely because it is measured, not computed. The tropical year and axial precession are geometric periods you can predict to the second or the year; the sunspot cycle is a statistical average of a physical process that refuses to keep exact time. Reading the two kinds of cycle side by side is a good way to see what "period" really means in astronomy.
For the underlying physics of spots, the dynamo, and the polarity flip, see the Learn lesson on the sunspot cycle, and the Sun object page for the star that drives it all.
Frequently asked questions
How long is the sunspot cycle?
On average about 11 years, measured from one minimum in sunspot number to the next. This is the Schwabe cycle. Individual cycles are not identical: over the modern record they have run anywhere from about 9 to 14 years, and the average spacing minimum to minimum is close to 10.7 years. It is an observed rhythm, not a fixed clock, so the length varies from cycle to cycle.
Why is the full solar magnetic cycle 22 years, not 11?
The Sun's magnetic polarity flips at each sunspot maximum. After one roughly 11-year Schwabe cycle the north and south magnetic poles have swapped, and the magnetic signs of spots have reversed. It takes a second cycle for the field to return to its original polarity. That full magnetic cycle, called the Hale cycle, is about 22 years, or two sunspot cycles back to back.
What solar cycle are we in now?
According to SILSO, we are in Solar Cycle 25. It began around December 2019 and passed its maximum in 2024 to 2025. Activity is now expected to decline toward the next minimum around 2030, which would mark the start of Solar Cycle 26. These dates are SILSO estimates and carry real uncertainty, since the timing of a cycle can only be pinned down clearly after it has passed.
Is the sunspot cycle an exact, predictable period?
No. Unlike an orbital period, the sunspot cycle cannot be computed from physics in advance. It is measured after the fact from the SILSO sunspot-number record. Both the length, roughly 9 to 14 years, and the peak strength vary from one cycle to the next in ways that are not fully predictable. Forecasts of the next maximum or minimum are always given with error bars rather than exact dates.
What causes sunspots and the cycle?
Sunspots are regions of concentrated magnetic field that block hot gas from below, making them cooler and darker than the surrounding surface. The cycle comes from a dynamo inside the Sun: because the equator rotates faster than the poles, the magnetic field is steadily wound up, driving activity to a maximum before the field reorganizes and decays to a minimum roughly 11 years apart.
When will Solar Cycle 25 end?
Solar Cycle 25 is expected to reach its minimum, handing over to Cycle 26, around 2030, but the exact timing is uncertain because cycles run anywhere from about 9 to 14 years. This is an estimate from the SILSO sunspot record and forecasts, not a fixed date.
Keep exploring
- Learn: the sunspot cycle: the dynamo and the polarity flip
- The Sun: the star that drives the cycle
- The tropical year: a computed period, for contrast
- Axial precession: the 25,920-year great year
- All astronomical cycles: where this sits among the rest