What is the Solar Cycle?
The solar cycle is the roughly 11-year variation in the Sun's magnetic activity. It is most visible in the number of sunspots: at solar maximum there are many sunspots and high activity; at solar minimum there are few or none. The cycle affects solar flares, CMEs, and solar wind, and thus space weather at Earth.
Sunspots and Activity
Sunspots are cooler, magnetically active regions on the photosphere. They are linked to flares and CMEs. When the cycle is at maximum, more sunspots mean more eruptions and a higher chance of geomagnetic storms and aurora. We are currently in Cycle 25, with maximum expected around 2024–2026.
Why 11 Years?
The cycle is driven by the Sun's dynamo—the generation of magnetic field by plasma motion in the interior. The period is not exactly 11 years; it can vary from about 9 to 14 years. Space weather forecasting takes the phase of the cycle into account when assessing the likelihood of strong events.
Sources and further reading
- NOAA – Sunspots and solar cycle – Official explanation and data
- NASA – Solar cycle – Solar cycle and space weather
- ESA Space Weather – European space weather programme